1. CENG 218 Classes and Data Structures

2. Dynamic Arrays in Data Structures
In the class for a data structure, we can add an Array object to the private section to store data
The functions of the data structure can expand or shrink the Array to conserve memory – this relieves the client from thinking about doing this

3. Dynamic Arrays in Data Structures (cont.)
In almost every data structure, we want functions for inserting and removing data
When dynamic arrays are used, the insertion function would add data to the array, while the removal function would “eliminate” data from the array (make it unusable)
When the array becomes full, we would want to do an expansion – when many elements have been removed, we would want to do a contraction, so that only the used elements remain

4. Array Expansion/Contraction
One possible method:
When an element is inserted by the client, increase the size of the array by 1
When an element is removed by the client, decrease the size of the array by 1
The problem with this method is that it is inefficient – every time an element is inserted or removed, the changeSize function is called…

5. changeSize Function 33 … 25 75 10 12 56 32 73 87
New element needs to be put into array, so changeSize function is called

6. changeSize Function (cont.) … 25 75 10 12 56 32 73 87 …
new array is made

7. changeSize Function (cont.) … 25 75 10 12 56 32 73 87 … 25 75 10 12 56 32 73 87
elements are copied over one by one using a for loop

8. changeSize Function (cont.)33 … 25 75 10 12 56 32 73 87 33
Then, the new element can be put in

9. changeSize Function (cont.) … 25 75 10 12 56 32 73 87 33
This process would take place every time a new element needs to be inserted.

10. changeSize Function (cont.) … 25 75 10 12 56 32 73 87 33
Likewise, when an element needs to be removed, this method contracts the array by one to conserve memory.

11. changeSize Function (cont.) … 25 75 10 12 56 32 73 87 33
Suppose the element at the end of the array needs to be removed.

12. changeSize Function (cont.) … 25 75 10 12 56 32 73 87 33 …
The changeSize function is called and a new, smaller array is made.

13. changeSize Function (cont.) … 25 75 10 12 56 32 73 87 33 … 25 75 10 12 56 32 73 87
The elements are copied over one by one, using a for loop.

14. changeSize Function (cont.) … 25 75 10 12 56 32 73 87
This method of array expansion/contraction is largely inefficient, because there is too much element copying.

15. A Better Method When the Array is full, double the size of it
When the number of elements used in the Array falls to 25% of the Array’s capacity, cut the size of the Array in half (it will be half full after the cut)

16. A Better Method (cont.) 25 75

17. A Better Method (cont.) 25 75 10

18. A Better Method (cont.) 25 75 10 12

19. A Better Method (cont.) 33 25 75 10 12
Array is full, so call changeSize function to double the size.

20. A Better Method (cont.) 25 75 10 12 33

21. A Better Method (cont.) 25 75 10 12 33 49 29 87
This array is full, but if we removed elements (made them inaccessible), we would cut the size of the array in half when its utilization drops to 25%

22. A Better Method (cont.) 25 75 10 12 33 49 29

23. A Better Method (cont.) 25 75 10 12 33 49

24. A Better Method (cont.) 25 75 10 12 33

25. A Better Method (cont.) 25 75 10 12

26. A Better Method (cont.) 25 75 10

27. A Better Method (cont.) 25 75
Array is 25% utilized, so use changeSize function to cut the size of the array in half.

28. A Better Method (cont.) 25 75
Array is 25% utilized, so use changeSize function to cut the size of the array in half.

29. A Better Method (cont.) 25 75
Using this method, memory is still conserved.
There is element copying every time changeSize is called, but it isn’t bad.

30. A Better Method (cont.) 25 75
It can be proven that, on average, there are no more than a couple of elements being copied on each insertion/deletion with this method.

31. Linked Structures
In a data structure, data is not always stored in an Array object
Sometimes it is best to store data in a linked structure (an alternative to an Array)
A linked structure consists of a group of nodes – each node is made from a struct.
An object of the Node struct contains an element of data.

32. A Node Class Template public class Node<T> { private T data;
The info member is for the data. It can
anything (T), but it is often the object of another type, used as a record of information.
public class Node<T> {
private T data;
private Node<T> next;
//public getters and setters
public Node(T inf){
next=null;
data=inf; }

33. A Node Struct Template (cont.)
public class Node<T> {
private T data;
private Node<T> next;
//public getters and setters
public Node(T inf){
next=null;
data=inf; }
The next reference(pointer) stores the address of a Node of the same type! This means that each node can point to another node.
data
next

34. Nodes
In a data structure, each node is made in the heap; therefore, a node can only be accessed by a reference(pointer).
The client does not deal with nodes.
When the client uses an insertion function, an element of data is passed into the function, and the function places it in a node.

35. Nodes (cont.)
When the client wants to retrieve data, the data in a node is returned to the client (but not the node itself).
The node struct template exists for use by the data structure.

36. Example of a Linked Structure
head
each node is divided into two sections, for the two members of the Node.

37. Example of a Linked Structure (cont.)
head
The left section is the data member.

38. Example of a Linked Structure (cont.)
head
The right section is the reference(pointer)(or reference) called “next”.

39. Example of a Linked Structure (cont.)
head
The head reference(pointer) would be saved in the private section of a data structure class.

40. Example of a Linked Structure (cont.)
head
The last node doesn’t point to another node, so its reference(pointer) (called next) is set to null (indicated by slash).

41. Linked Lists
The arrangement of nodes in the linked structure on the previous slide is often called a linked list.
We can access any element of the linked list, for retrieval of information.
We can also remove any element from the linked list (which would shorten the list).
We can also insert any element into any position in the linked list.

42. Linked List Advantages
Assume we have a list 100,000 elements … … 5 3 7 2 1
Removing an element from the middle of a linked list is fast.

43. Linked List Advantages (cont.)… … 5 3 2 1 7
Removing an element from the middle of a linked list is fast.

44. Linked List Advantages (cont.)
Assume we have an array having 100,000 elements … … 25 75 10 12 33 49 29 87
Removing elements from the middle of an array (without leaving gaps) is more problematic.

45. Linked List Advantages (cont.)
Assume we have an array having 100,000 elements … … 25 75 10 33 49 29 87
Removing elements from the middle of an array (without leaving gaps) is more problematic.

46. Linked List Advantages (cont.)
Assume we have an array having 100,000 elements … … 25 75 10 33 49 29 87
A loop must be used to slide each element on the right one slot to the left, one at a time…

47. Linked List Advantages (cont.)
Assume we have an array having 100,000 elements … … 25 75 10 33 49 29 87

48. Linked List Advantages (cont.)
Assume we have an array having 100,000 elements … … 25 75 10 33 49 29 87

49. Linked List Advantages (cont.)
Assume we have an array having 100,000 elements … … 25 75 10 33 49 29 87

50. Linked List Advantages (cont.)
Assume we have an array having 100,000 elements … … 25 75 10 33 49 29 87

51. Linked List Advantages (cont.)
Assume we have an array having 100,000 elements … … 25 75 10 33 49 29 87
Only 100,000 more to go!

52. Linked List Advantages (cont.)
Linked lists also waste less memory for large elements (records of information).
Wasted memory is memory space in the data structure not used for data.
In arrays, the wasted memory is the part of the array not being utilized.
In linked lists, the wasted memory is the reference(pointer) in each node.

53. Linked List Advantages (cont.)
head
Linked List
Array

54. Accessing info head To access the info in the first node:
head.getData()

55. Accessing info (cont.) head To access the info in the second node:
head.getLink().getData()

56. Finding the Mercedes head…
Mercedes
Consider a linked list, where the info member (left half of blue box) is a CarType object
We wish to find a Mercedes stored in one of the objects.

57. CarType Class public class CarType { private double price;
private int year;
private String maker;
public CarType(double price, int year, String maker) {
this.price = price;
this.year = year;
this.maker = maker; }
public double getPrice() {
return price;
public void setPrice(double price) {
public int getYear() {
return year;
public void setYear(int year) {
public String getMaker() {
return maker;
public void setMaker(String maker) {
@Override
public String toString() {
return "CarType [price=" + price + ", year=" + year + ", maker=" + maker + "]";
public boolean equals(Object arg0) {
if(arg0!=null){
if(arg0 instanceof CarType){
CarType other=(CarType)arg0;
return maker.equals(other.maker);
return false;

58. Finding the Mercedes (cont.)
head …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

59. Finding the Mercedes (cont.)
head …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

60. Finding the Mercedes (cont.)
head
item
maker:
price:
year: …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

61. Finding the Mercedes (cont.)
item
head
maker: Mercedes
price:
year: …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

62. Finding the Mercedes (cont.)
head
item
maker: Mercedes
price:
year: …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

63. Finding the Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

64. Finding the Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

65. Finding the Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

66. Finding the Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

67. Finding the Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Mercedes
Loop repeats,
walk moves through list
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

68. Finding the Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

69. Finding the Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Mercedes
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();
FOUND!

70. Finding the Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Mercedes
Loop stops
walk points to the node containing Mercedes
Can return walk.getData() to the client, so that the client can access data members, such as price

71. What if no Mercedes?
The code we looked at assumes there is a Mercedes in the linked list
The following slides show the error that will occur if Mercedes is not in the linked list…

72. No Mercedes item head walk maker: Mercedes price: year: …
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

73. No Mercedes (cont.) item head walk maker: Mercedes price: year: …
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

74. No Mercedes (cont.) item head walk maker: Mercedes price: year: …
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

75. No Mercedes (cont.) item head walk maker: Mercedes price: year: …
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

76. No Mercedes (cont.) item head walk maker: Mercedes price: year: …
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

77. No Mercedes (cont.) item head walk is set to null maker: Mercedes
price:
year: …
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

78. No Mercedes (cont.) item head walk is set to null maker: Mercedes
price:
year: …
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();

79. No Mercedes (cont.) item head walk is set to null maker: Mercedes
price:
year: …
CarType item=new CarType(…….);
item.setMaker(“Mercedes”);
Node<CarType> walk = head;
while ( ! walk.getData().equals(item ) )
walk=walk.getLink();
Runtime error!
Since walk is null .equals method can not be invoked.

80. Finding a Possible Mercedes
head
item
maker: Mercedes
price:
year: …
Let’s solve the problem, but let’s assume that item is passed in as a parameter (of type DataType). This is normally what would happen.

81. Finding a Possible Mercedes (cont.)
head
item
maker: Mercedes
price:
year: …
Node<CarType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }

82. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) ) // overloaded ==
found = true;
if ( !found )
walk = walk.getNext(); }

83. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) ) // overloaded ==
found = true;
if ( !found )
walk = walk.getNext(); }

84. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

85. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

86. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

87. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

88. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

89. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

90. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false
Notice that found is only set to true if Mercedes is found …

91. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false
then, !found is false and the loop exits

92. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false
If Mercedes is not found, ptr eventually gets set to null, as before.

93. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false
After going through the loop several times…

94. Finding a Possible Mercedes (cont.)
head
walk
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

95. Finding a Possible Mercedes (cont.)
head
walk is set to null
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

96. Finding a Possible Mercedes (cont.)
head
walk
is set to null
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

97. Finding a Possible Mercedes (cont.)
head
walk
is set to null
item
maker: Mercedes
price:
year: …
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false
Exit from loop with no runtime error

98. Another Case What if the linked list is empty to begin with?
Try to consider all possible cases
When a linked list is empty, the head reference(pointer) should always be set to null
The head reference(pointer) would be set to null inside the constructor, when an empty linked list is first made

99. Empty List Case item head is set to null maker: Mercedes price: year:
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }

100. Empty List Case (cont.) item head is set to null maker: Mercedes
price:
year:
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
SAME CODE

101. Empty List Case (cont.) item head is set to null maker: Mercedes
price:
year:
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }

102. Empty List Case (cont.) item head is set to null maker: Mercedes
price:
year:
walk is set to null
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }

103. Empty List Case (cont.) item head is set to null maker: Mercedes
price:
year:
walk is set to null
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }

104. Empty List Case (cont.) item head is set to null maker: Mercedes
price:
year:
walk is set to null
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

105. Empty List Case (cont.) item head is set to null maker: Mercedes
price:
year:
operator ==
walk is set to null
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false

106. Empty List Case (cont.) item head is set to null maker: Mercedes
price:
year:
operator ==
walk is set to null
Node<DataType> walk = head;
bool found = false;
while (walk != null && !found ) {
if ( walk.getData().equals( item ) )
found = true;
if ( !found )
walk = walk.getNext(); }
found: false
Exit loop without runtime error

107. Inserting a New Node
Let’s assume that we want to insert a new node at the beginning of a linked list
Assume that the client passes in a parameter called element (of type DataType)
We would like to place the element into a node and insert the node at the beginning of the linked list

108. Inserting a Node
element
head

109. Inserting a Node (cont.)
element
head
All new nodes must be made in the heap, SO…

110. Inserting a Node (cont.)
element
head
Node<DataType> ptr = new Node<DataType>();

111. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();

112. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
Now we have to store element into the node

113. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

114. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

115. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

116. Inserting a Node (cont.)
element
head
Now we have to think about how to make the reference(pointer) called “next” point to the first node in the list, to link it in
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

117. Inserting a Node (cont.)
element
head
You can’t successfully write code like this without thinking about addresses.
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

118. Inserting a Node (cont.)
element
head
REMEMBER…when you want to change the way a reference(pointer) points, you HAVE to assign a different address to it
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

119. Inserting a Node (cont.)
element
head
Right now, the reference(pointer) called “next” doesn’t have a valid address assigned to it.
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

120. Inserting a Node (cont.)
element
head
To store the correct address in it, we have to find the address of the first node of the linked list.
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

121. Inserting a Node (cont.)
element
head
Where is the address of the first node stored?
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

122. Inserting a Node (cont.)
element
head
Now think, the address would be stored in something that points to it. So where is it stored?
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

123. Inserting a Node (cont.)
element
head
ptr
That’s right, in the head reference(pointer).
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

124. Inserting a Node (cont.)
element
head
So now, all we have to do is copy that address into the reference(pointer) called “next”
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

125. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);

126. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);

127. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);

128. Inserting a Node (cont.)
element
head
Well, it’s been inserted. But head should point to the first node now.
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);

129. Inserting a Node (cont.)
element
head
REMEMBER…when you want to change the way a reference(pointer) points, you have to assign a different address to it
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);

130. Inserting a Node (cont.)
element
head
We’d like head to point to the new node, so what stores the address of the new node?
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);

131. Inserting a Node (cont.)
element
head
That’s right, ptr. So now all we have to do is assign the address stored in ptr to the head reference(pointer).
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);

132. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);

133. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);
head=ptr;

134. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);
head=ptr;

135. Inserting a Node (cont.)
element
head
ptr
Node<DataType> ptr = new Node<DataType>();
ptr.setData(element);
ptr.setNext( head);
head=ptr;

136. REMEMBER…
Always use drawings when working with linked lists, until you become an expert
When you want to change the way a reference(pointer) points, you have to assign a different address to it
You can find the address you need by looking at other reference(pointer)s (remember that they store addresses)

137. Inserting into the Middle (between nodes) of a Linked List
Suppose we know that there is a Mercedes in a linked list
We would like to insert a node containing Honda right after it
We first find the Mercedes, using code that we looked at before

138. Inserting a Node head element maker: Mercedes price: year: …
Node<DataType> ptr = head;
while ( ptr.getData.equals(element) ) // element is a parameter
ptr = ptr.getNext();

139. Inserting a Node (cont.)
head
element
maker: Mercedes
price:
year: …
Mercedes
After this code executes, ptr points to the node that has Mercedes.
Node<DataType> ptr = head;
while ( ptr.getData.equals(element) ) // element is a parameter
ptr = ptr.getNext();

140. Inserting a Node (cont.)
head
element
ptr
maker: Mercedes
price:
year: …
Mercedes
After this code executes, ptr points to the node that has Mercedes.
Node<DataType> ptr = head;
while ( ptr.getData.equals(element) ) // element is a parameter
ptr = ptr.getNext();

141. Inserting a Node (cont.)
head
element
ptr
maker: Mercedes
price:
year: …
Mercedes
Now we would like to insert a CarType object called elementToInsert (containing Honda), which would also be passed in as a parameter, right after the Mercedes

142. Inserting a Node (cont.)
head
ptr
maker: Honda
price: 5000
year: 1985 …
Mercedes
elementToInsert

143. Inserting a Node (cont.)
head
ptr
maker: Honda
price: 5000
year: 1985
operator != …
Mercedes
elementToInsert
Well, all new nodes are created in the heap, SO…..

144. Inserting a Node (cont.)
head
ptr
maker: Honda
price: 5000
year: 1985
operator != …
Mercedes
elementToInsert
(object of Car Type)
First create a new Node for new Data
Node<DataType> newNode = new Node<DataType>(elementToInsert);

145. Inserting a Node (cont.)
head
ptr
maker: Honda
price: 5000
year: 1985 …
Mercedes
elementToInsert
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);

146. Inserting a Node (cont.)
head
ptr
maker: Honda
price: 5000
year: 1985 …
Mercedes
elementToInsert
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);

147. Inserting a Node (cont.)
head
ptr
maker: Honda
price: 5000
year: 1985 …
Mercedes
elementToInsert
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);

148. Inserting a Node (cont.)
head
ptr …
Mercedes
newNode
Node<DataType> *newNode = new Node<DataType>;
newNode->info = elementToInsert;

149. Inserting a Node (cont.)
head
ptr
Now, what we want is shown by the dashed arrows; this would cause the insertion of the node …
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);

150. Inserting a Node (cont.)
head
ptr
We have two reference(pointer)s we need to change – but we have to be careful about the way we change them …
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);

151. Inserting a Node (cont.)
head
ptr
If we change the left reference(pointer) first, we will no longer be able to access the last node (memory leak) …
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);

152. Inserting a Node (cont.)
head
ptr
So, we first have to assign the address of the last node into the “next” reference(pointer) of the new node …
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);

153. Inserting a Node (cont.)
head
ptr
Where is the address of the last node stored? …
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);

154. Inserting a Node (cont.)
head
ptr
That’s right, it is stored in ptr.next …
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);

155. Inserting a Node (cont.)
head
ptr …
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);
newNode.setNext( ptr.getNext());

156. Inserting a Node (cont.)
head
ptr …
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);
newNode.setNext( ptr.getNext());

157. Inserting a Node (cont.)
head
ptr …
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);
newNode.setNext( ptr.getNext());
ptr.setNext (newNode);

158. Inserting a Node (cont.)
head
ptr …
Mercedes
Mercedes
newNode
Node<DataType> newNode = new Node<DataType>(elementToInsert);
newNode.setNext( ptr.getNext());
ptr.setNext (newNode);

159. Removing a Node
Suppose we definitely know there is a Mercedes in the linked list and we wish to remove the node that contains it
We need to find the node first

160. Removing a Node (cont.)
head …
Mercedes

161. Removing a Node (cont.)
ptr
head …
Mercedes

162. Removing a Node (cont.) ptr head …
Mercedes
When it is found, we need to join the node in front of it to the node after it.

163. Removing a Node (cont.) ptr head …
Mercedes
When it is found, we need to join the node in front of it to the node after it.

164. Removing a Node (cont.) ptr head …
Mercedes
But how can we access the “next” reference(pointer) of the node in front, so we can change the address it stores?
(we can’t)

165. Removing a Node (cont.) ptr head …
Mercedes
The way to solve the problem is by having ptr stop on the node BEFORE the node that has Mercedes

166. Removing a Node (cont.)
ptr
head …
Mercedes

167. Removing a Node (cont.)
ptr
head …
Mercedes

168. Removing a Node (cont.) ptr head …
Mercedes
If ptr stops here, then we CAN change the address stored in the “next” reference(pointer). So we have to set up a loop appropriately.

169. Removing a Node (cont.)
head …
Mercedes

170. Removing a Node (cont.) head … element contains Mercedes
Node<DataType> walk = head;
Node <DataType>prev=null;
while (walk!= null ) && (walk.getData().equals(element) {
prev=walk;
walk=walk.getNext(); }

171. Removing a Node (cont.) head …
Mercedes
passed in from the client as a parameter
Node<DataType> walk = head;
Node <DataType>prev=null;
while (walk!= null ) && (walk.getData().equals(element) {
prev=walk;
walk=walk.getNext(); }

172. Removing a Node (cont.) head …
Mercedes
BUT…what if Mercedes is in the first node?

173. Removing a Node (cont.) head …
Mercedes
BUT…what if Mercedes is in the first node?
We need to handle the first node differently.

174. Removing a Node (cont.)
head …
Mercedes

175. Removing a Node (cont.) head … Node<DataType> ptr = head;
Mercedes
Node<DataType> ptr = head;
if ( head.getData().equals( element ) )
head = head.getNext();

176. Removing a Node (cont.) head … Node<DataType> ptr = head;
Mercedes
Node<DataType> ptr = head;
if ( head!=null && head.getData().equals( element ) )
head = head.getNext();

177. Removing a Node (cont.) ptr head … Node<DataType> ptr = head;
Mercedes
Node<DataType> ptr = head;
if ( head!=null && head.getData().equals( element ) )
head = head.getNext();

178. Removing a Node (cont.) ptr head … Node<DataType> ptr = head;
Mercedes
Node<DataType> ptr = head;
if ( head!=null && head.getData().equals( element ) )
head = head.getNext();

179. Removing a Node (cont.) ptr head … Node<DataType> ptr = head;
Mercedes
Node<DataType> ptr = head;
if ( head!=null && head.getData().equals( element ) )
head = head.getNext();

180. Removing a Node (cont.) ptr head … Node<DataType> ptr = head;
Mercedes
Node<DataType> ptr = head;
if ( head!=null && head.getData().equals( element ) )
head = head.getNext();

181. Removing a Node (cont.) ptr head … Node<DataType> ptr = head;
Well, head points to the beginning of the new linked list, node pointed by ptr will be göne to garbage
ptr
head …
Mercedes
Node<DataType> ptr = head;
if ( head!=null && head.getData().equals( element ) )
head = head.getNext();

182. Removing a Node (cont.)
ptr
head …

183. Removing a Node (cont.) ptr head … Now, let’s consider the other case.
Node<DataType> ptr = head;
if ( head!=null && head.getData().equals( element ) )
head = head.getNext();

184. Removing a Node (cont.) head … Mercedes
Node<DataType> ptr = head;
if ( head!=null && head.getData().equals( element ) )
head = head.getNext();
else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }

185. Removing a Node (cont.) head … Mercedes
This is the loop that we thought of before.
else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }

186. Removing a Node (cont.) head … Mercedes
It will find the node BEFORE the node that has Mercedes.
else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }

187. Removing a Node (cont.) walk prev head … Mercedes
It will find the node BEFORE the node that has Mercedes.
prev
walk
head …
Mercedes
else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }

188. Removing a Node (cont.) walk prev head …
Mercedes
Now we need to join the node before Mercedes to the node after Mercedes
else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }

189. Removing a Node (cont.) walk prev head … Mercedes else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }
if(walk!=null) //if target is found
prev.setNext(walk.getNext();

190. Removing a Node (cont.) walk prev head … Mercedes else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }
if(walk!=null) //if target is found
prev.setNext(walk.getNext();

191. Removing a Node (cont.) walk prev head … Mercedes else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }
if(walk!=null) //if target is found
prev.setNext(walk.getNext();

192. Removing a Node (cont.) walk prev head … Mercedes else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }
if(walk!=null) //if target is found
prev.setNext(walk.getNext();

193. Removing a Node (cont.) walk prev head … Mercedes
else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }
if(walk!=null) //if target is found
prev.setNext(walk.getNext();
But how will we free the node that has Mercedes?
No: Garbage Collector will handle it

194. Removing a Node (cont.) walk prev head … else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }
if(walk!=null) //if target is found
prev.setNext(walk.getNext();

195. What If? What if Mercedes is the last node in the linked list
Would our code still work?
Try to consider every possible situation in code design

196. Removing the Last Node walk prev head …
Mercedes
After looping, ptr stops on the next-to-the-last node
else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }
if(walk!=null) //if target is found
prev.setNext(walk.getNext();

197. Removing the Last Node (cont.)
prev
walk
head …
Mercedes
else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }
if(walk!=null) //if target is found
prev.setNext(walk.getNext(); //will disconnect last node from linked list

198. Removing the Last Node (cont.)
walk
prev
head …
Mercedes
Java garbage collector will remove last node
else {
while ( walk!=null && !walk.getData().equals(element ) ){
prev=walk;
walk = walk.getNext(); }
if(walk!=null) //if target is found
prev.setNext(walk.getNext(); //will disconnect last node from linked list

199. Removing the Last Node (cont.)
prev
head …
The code works in removing the last node.

200. Working With Linked Lists
As you can see, sometimes you have to do a lot of thinking and problem-solving when working with linked lists
It is not always obvious how to write code
You can’t memorize the code, because it will not quite fit situations that you will encounter
It is a matter of using logic (and knowing a few tricks of the trade)

201. Code for Removing a Node
Here is the resulting code for removing a node. It is assumes the node we are looking for is in the linked list.

202. Code for Removing a Node (cont.)
This code can be simplified by using a dummy head node
A header node is like any other node, except it doesn’t contain data.
Since we know the first node doesn’t contain data, it can’t contain Mercedes.

203. Removing a Node
But this code assumes that there definitely is a Mercedes in the linked list
Let’s refine it a little
Suppose we are not really sure if there is a Mercedes in the linked list to delete
Or suppose the linked list is empty to begin with
Always try to handle every case

204. Refining Code with Header Node

205. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next->info != element )
ptr = ptr->next;
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2;
We’ll use our found variable, like before.

206. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next->info != element )
ptr = ptr->next;
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2;
This will give us a runtime error if we have an empty list. Let’s test for it in a loop heading.

207. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next->info != element )
ptr = ptr->next;
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2;
We’ll make a new loop and shove this part inside.

208. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next != null ) {
while ( ptr->next->info != element )
ptr = ptr->next;
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2; }

209. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next != null ) {
while ( ptr->next->info != element )
ptr = ptr->next;
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2; }
Now we want the removal code if ptr->next->info IS equal to element

210. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next != null ) {
if ( ptr->next->info == element )
ptr = ptr->next;
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2; }
Now we want the removal code if ptr->next->info IS equal to element

211. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next != null ) {
if ( ptr->next->info == element ) {
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2; }

212. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next != null ) {
if ( ptr->next->info == element ) {
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2; }
If we remove a node, we need to break out of the loop.

213. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next != null && !found ) {
if ( ptr->next->info == element ) {
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2;
found = true; }
If we remove a node, we need to break out of the loop.

214. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next != null && !found ) {
if ( ptr->next->info == element ) {
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2;
found = true; }
Now, we just need to advance ptr if we didn’t remove a node.

215. Refining Code with Header Node (cont.)
Node<DataType> *ptr = head;
bool found = false;
while ( ptr->next != null && !found ) {
if ( ptr->next->info == element ) {
Node<DataType> *ptr2 = ptr->next;
ptr->next = ptr2->next;
delete ptr2;
found = true; }
if ( !found )
ptr = ptr->next;
Final result.

216. Linked List vs. Arrays
When computer scientists decide on whether or not to use an array or linked list for data, the decision is usually based on two factors:
Speed
Conservation of Memory (RAM)

217. Speed
In some situations, an array can be faster than a linked list, such as when a calculated index is used to access an element
In other situations, a linked list can be faster than an array, such as when removing an element from the middle (as we saw before)
we usually need to search for the element to remove, but we search for it in both the array and linked list