1. Linked Lists (continued)
October 11, 2017
Hassan Khosravi / Geoffrey Tien

2. Example
Linked list for hockey players
Recall: nodes defined as structures with attributes, and a pointer to the next node
struct Player {
int jersey_number;
char* name;
struct Player* next; };
typedef struct Player Player;
int main() {
Player* head_list1 = NULL;
Player* head_list2 = NULL;
Player gretzky = {99,
"Wayne Gretzky", NULL};
// example 1
head_list1 = &gretzky;
displayList(head_list1);
// example 2
head_list2 = insertAtHead(head_list2,
22, "Daniel Sedin");
33, "Henrik Sedin");
displayList(head_list2); }
Note that head_list1 only needs a pointer type, so syntactically we could assign it a pointer to a local Player variable
October 11, 2017
Hassan Khosravi / Geoffrey Tien

3. Hockey example continued
insertAtHead
insertAtHead should insert a new node at the head of a (possibly empty) list, and return the node as the new head
will this code work? Why or why not?
Player* insertAtHead(Player* head, int player_number, char* player_name) {
Player new_node;
new_node->jersey_number = player_number;
new_node->name = player_name;
new_node->next = head; // point to current head of list
printf("Node was added.\n\n");
return &new_node; // the new node becomes the new head of list }
October 11, 2017
Hassan Khosravi / Geoffrey Tien

4. Hockey example continued
insertAtHead
insertAtHead should insert a new node at the head of a (possibly empty) list, and return the node as the new head
is this better?
Player* insertAtHead(Player* head, int player_number, char* player_name) {
Player* new_node;
new_node = (Player*) malloc(sizeof(Player));
new_node->jersey_number = player_number;
new_node->name = player_name;
new_node->next = head; // point to current head of list
printf("Node was added.\n\n");
return new_node; // the new node becomes the new head of list }
October 11, 2017
Hassan Khosravi / Geoffrey Tien

5. Hockey example continued
A function to iterate through a (possibly empty) linked list, starting from the head of the list, and printing out information from each node
void displayList(Player* node) {
int k = 0;
while (node) { // loop breaks when node becomes NULL
printf("Node %d is: %s, Jersey number %d\n",
k, node->name, node->jersey_number);
node = node->next;
k++; }
printf("There are %d node(s) in the list.\n\n", k);
See hockey_players_linked_list_V1.c
October 11, 2017
Hassan Khosravi / Geoffrey Tien

6. Hassan Khosravi / Geoffrey Tien
Quick exercise
Inserting into a list
Consider the following linked list, and possible commands in the box
W: current->next = new;
X: current = current->next;
Y: new->next = current->next;
Z: current = new;
Assuming we wish to keep the list ordered, which of the command sequences correctly inserts the new node into the list?
X X X Y W
X X X X W Y
X X X W Y
X X X W Z Y
None of the above 1 2 3 4 6 7
current 5
new
October 11, 2017
Hassan Khosravi / Geoffrey Tien

7. Hassan Khosravi / Geoffrey Tien
Quick exercise
Removing from a list
Consider the following linked list, and possible commands in the box
V: current = current->next;
W: prev = prev->next;
X: prev->next = current->next;
Y: current->next = prev->next;
Z: free(current); current = NULL;
Which of the command sequences correctly removes the node containing "3" from the list?
V W V Y Z
W V W X Z
V W V X Z
V V W W Y Z
None of the above 1 2 3 4 6 7
prev
current
October 11, 2017
Hassan Khosravi / Geoffrey Tien

8. Comparison of worst case complexities
Assume we know the number of entries in the arrays
also assume current position (in lists) is known
Operation
Array (unordered)
Array (ordered)
Linked list (unordered)
Linked list (ordered
Insert at front
Insert at back, using head ptr
Insert after current position
Search for a value
Remove at current position
October 11, 2017
Hassan Khosravi / Geoffrey Tien

9. Hassan Khosravi / Geoffrey Tien
Extra pointers
Notice how the operations at the end of the list have (relatively) poor complexity, involving a complete traversal of the list
we can give ourselves a tail pointer, for very little additional overhead
head 1 2 3 4 6 7
tail 9
With a tail pointer, what is the complexity inserting into an ordered list, if the item is known to be larger than the largest so far? What if the item is not necessarily larger than the largest item?
new
October 11, 2017
Hassan Khosravi / Geoffrey Tien

10. Readings for this lesson
Thareja
Chapter 6
Next class: other flavours of linked lists
October 11, 2017
Hassan Khosravi / Geoffrey Tien