© M. Gross, ETH Zürich, 2014 Informatik I für D-MAVT (FS 2014) Exercise 11 – Data Structures

© M. Gross, ETH Zürich, 2014 Agenda  Linked Lists  Queues  Stacks  Exercise

© M. Gross, ETH Zürich, Linked Lists  Collection of nodes  Two components for each node  to store the data  to store the “next” linked node  Last node has no linked node  Referenced by NULL  Structure of node declaration c++ struct nodeType { int data; nodeType *next; }; nodeType *head; head

© M. Gross, ETH Zürich, Linked Lists Operations  Traversing a list  Use other pointer similar to *head not to lose reference to beginning of list  Finding an element in the list  Traverse the list until you find the element (here 12)  Do something if not found nodeType *current; current = head; while (current != NULL) { cout data next; } nodeType *current; current = head; int element = 12; while (current != NULL) { if(current->data == element) break; current = current->next; } if(current == NULL) cout <<"element not found“ << endl;

© M. Gross, ETH Zürich, Linked Lists Operations  Inserting a new node  Create a new node  Determine insertion position and assign it to current  Make the new node point to the same node that current is pointing to  Make current now point to the new node nodeType *newNode; newNode = new nodeType; newNode->data = 37; newNode->next = current->next; current- >next = newNode;

© M. Gross, ETH Zürich, Linked Lists Operations  Deleting a node  Determine the node to be removed (deleteNode) and point current to the node prior to that node  Create a pointer to point to the node you want to delete (i.e *deleteNode)  Make current’s link now point to deleteNode’s link  delete the node from memory Assuming current is at correct position nodeType *deleteNode; deleteNode = current->next; current->next = deleteNode->next; delete deleteNode;

© M. Gross, ETH Zürich, Building Linked Lists  Backward approach // Init the list nodeType *head; nodeType *newNode; int num; head = NULL; // Build the list using the backward approach for (int i=0; i<3; i++) { cout << "Enter number :"; cin >> num; newNode = new nodeType; // Create the new node newNode->data = num; // and assign its data value newNode->next = head; // make its link point to the // front of the list head = newNode; // make the head now be the // newNode }

© M. Gross, ETH Zürich, 2014 Doubly Linked Lists  Similar to single linked lists but  Each node has a connection to the previous one  List can be traversed also backwards  Can reach a3 from a1 and vice versa 8 struct nodeType { int data; nodeType *next; nodeType *prev; }; nodeType *head;

© M. Gross, ETH Zürich, Queues  Like linked lists  Add new elements at the end  Remove elements from the head struct element { int value; // The value of the element struct element *next; // Pointer to the next element }; typedef struct element Node; Node *head = NULL; //Pointer to first element Node *tail = NULL; //Pointer to last element a1a1 a2a2 a3a3 anan null headtail

© M. Gross, ETH Zürich, Queues  add element  remove element v a1a1 a2a2 a3a3 headtail null tail->next = v; tail = v; v -> next = NULL; Node *v = head; head = head->next; delete v; a1a1 a2a2 a3a3 null head tail v

© M. Gross, ETH Zürich, Stacks  “One-sided queues”  Add to and remove from the “top” by pushing/popping  The only element that is reachable is the top element! a0a0 a1a1 a2a2 a3a3 a4a4 top

© M. Gross, ETH Zürich, Stacks  add element  remove element v a1a1 a2a2 a3a3 head null v->next = head; head = v; Node *v = head; head = head->next; delete v; a1a1 a2a2 a3a3 null head v

© M. Gross, ETH Zürich, Stacks vs Queues  Queues:  Work in FIFO (first-in-first-out) fashion  Store two pointers  Add/removal using different pointers  Operating systems: Jobs wait in a queue for CPU time  Printers: Incoming jobs end up in a queue  Stacks:  Work in LIFO (last-in-first-out) fashion  Store only one pointer  Add/removal from top only  Evaluating Arithmetic Operations  Function calls: They are put in a stack by the compiler