Doubly Linked List

Doubly Linked List

@@ -0,0 +1,275 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+struct node {
+   int data;
+   int key;
+
+   struct node *next;
+   struct node *prev;
+};
+
+//this link always point to first Link
+struct node *head = NULL;
+
+//this link always point to last Link 
+struct node *last = NULL;
+
+struct node *current = NULL;
+
+//is list empty
+bool isEmpty() {
+   return head == NULL;
+}
+
+int length() {
+   int length = 0;
+   struct node *current;
+
+   for(current = head; current != NULL; current = current->next){
+      length++;
+   }
+
+   return length;
+}
+
+//display the list in from first to last
+void displayForward() {
+
+   //start from the beginning
+   struct node *ptr = head;
+
+   //navigate till the end of the list
+   printf("\n[ ");
+
+   while(ptr != NULL) {        
+      printf("(%d,%d) ",ptr->key,ptr->data);
+      ptr = ptr->next;
+   }
+
+   printf(" ]");
+}
+
+//display the list from last to first
+void displayBackward() {
+
+   //start from the last
+   struct node *ptr = last;
+
+   //navigate till the start of the list
+   printf("\n[ ");
+
+   while(ptr != NULL) {    
+
+      //print data
+      printf("(%d,%d) ",ptr->key,ptr->data);
+
+      //move to next item
+      ptr = ptr ->prev;
+
+   }
+
+}
+
+//insert link at the first location
+void insertFirst(int key, int data) {
+
+   //create a link
+   struct node *link = (struct node*) malloc(sizeof(struct node));
+   link->key = key;
+   link->data = data;
+
+   if(isEmpty()) {
+      //make it the last link
+      last = link;
+   } else {
+      //update first prev link
+      head->prev = link;
+   }
+
+   //point it to old first link
+   link->next = head;
+
+   //point first to new first link
+   head = link;
+}
+
+//insert link at the last location
+void insertLast(int key, int data) {
+
+   //create a link
+   struct node *link = (struct node*) malloc(sizeof(struct node));
+   link->key = key;
+   link->data = data;
+
+   if(isEmpty()) {
+      //make it the last link
+      last = link;
+   } else {
+      //make link a new last link
+      last->next = link;     
+
+      //mark old last node as prev of new link
+      link->prev = last;
+   }
+
+   //point last to new last node
+   last = link;
+}
+
+//delete first item
+struct node* deleteFirst() {
+
+   //save reference to first link
+   struct node *tempLink = head;
+
+   //if only one link
+   if(head->next == NULL){
+      last = NULL;
+   } else {
+      head->next->prev = NULL;
+   }
+
+   head = head->next;
+   //return the deleted link
+   return tempLink;
+}
+
+//delete link at the last location
+
+struct node* deleteLast() {
+   //save reference to last link
+   struct node *tempLink = last;
+
+   //if only one link
+   if(head->next == NULL) {
+      head = NULL;
+   } else {
+      last->prev->next = NULL;
+   }
+
+   last = last->prev;
+
+   //return the deleted link
+   return tempLink;
+}
+
+//delete a link with given key
+
+struct node* delete(int key) {
+
+   //start from the first link
+   struct node* current = head;
+   struct node* previous = NULL;
+
+   //if list is empty
+   if(head == NULL) {
+      return NULL;
+   }
+
+   //navigate through list
+   while(current->key != key) {
+      //if it is last node
+
+      if(current->next == NULL) {
+         return NULL;
+      } else {
+         //store reference to current link
+         previous = current;
+
+         //move to next link
+         current = current->next;             
+      }
+   }
+
+   //found a match, update the link
+   if(current == head) {
+      //change first to point to next link
+      head = head->next;
+   } else {
+      //bypass the current link
+      current->prev->next = current->next;
+   }    
+
+   if(current == last) {
+      //change last to point to prev link
+      last = current->prev;
+   } else {
+      current->next->prev = current->prev;
+   }
+
+   return current;
+}
+
+bool insertAfter(int key, int newKey, int data) {
+   //start from the first link
+   struct node *current = head; 
+
+   //if list is empty
+   if(head == NULL) {
+      return false;
+   }
+
+   //navigate through list
+   while(current->key != key) {
+
+      //if it is last node
+      if(current->next == NULL) {
+         return false;
+      } else {           
+         //move to next link
+         current = current->next;
+      }
+   }
+
+   //create a link
+   struct node *newLink = (struct node*) malloc(sizeof(struct node));
+   newLink->key = newKey;
+   newLink->data = data;
+
+   if(current == last) {
+      newLink->next = NULL; 
+      last = newLink; 
+   } else {
+      newLink->next = current->next;         
+      current->next->prev = newLink;
+   }
+
+   newLink->prev = current; 
+   current->next = newLink; 
+   return true; 
+}
+
+void main() {
+   insertFirst(1,10);
+   insertFirst(2,20);
+   insertFirst(3,30);
+   insertFirst(4,1);
+   insertFirst(5,40);
+   insertFirst(6,56); 
+
+   printf("\nList (First to Last): ");  
+   displayForward();
+
+   printf("\n");
+   printf("\nList (Last to first): "); 
+   displayBackward();
+
+   printf("\nList , after deleting first record: ");
+   deleteFirst();        
+   displayForward();
+
+   printf("\nList , after deleting last record: ");  
+   deleteLast();
+   displayForward();
+
+   printf("\nList , insert after key(4) : ");  
+   insertAfter(4,7, 13);
+   displayForward();
+
+   printf("\nList  , after delete key(4) : ");  
+   delete(4);
+   displayForward();
+}