Different ways to insert in Doubly Linked List

Author: sudesh1611

Data Structures/DoublyLinkedList/Insertion.c

@@ -0,0 +1,144 @@
+// A complete working C program to demonstrate all insertion methods 
+#include <stdio.h> 
+#include <stdlib.h> 
+  
+// A linked list node 
+struct Node { 
+    int data; 
+    struct Node* next; 
+    struct Node* prev; 
+}; 
+  
+/* Given a reference (pointer to pointer) to the head of a list 
+   and an int, inserts a new node on the front of the list. */
+void push(struct Node** head_ref, int new_data) 
+{ 
+    /* 1. allocate node */
+    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); 
+  
+    /* 2. put in the data  */
+    new_node->data = new_data; 
+  
+    /* 3. Make next of new node as head and previous as NULL */
+    new_node->next = (*head_ref); 
+    new_node->prev = NULL; 
+  
+    /* 4. change prev of head node to new node */
+    if ((*head_ref) != NULL) 
+        (*head_ref)->prev = new_node; 
+  
+    /* 5. move the head to point to the new node */
+    (*head_ref) = new_node; 
+} 
+  
+/* Given a node as prev_node, insert a new node after the given node */
+void insertAfter(struct Node* prev_node, int new_data) 
+{ 
+    /*1. check if the given prev_node is NULL */
+    if (prev_node == NULL) { 
+        printf("the given previous node cannot be NULL"); 
+        return; 
+    } 
+  
+    /* 2. allocate new node */
+    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); 
+  
+    /* 3. put in the data  */
+    new_node->data = new_data; 
+  
+    /* 4. Make next of new node as next of prev_node */
+    new_node->next = prev_node->next; 
+  
+    /* 5. Make the next of prev_node as new_node */
+    prev_node->next = new_node; 
+  
+    /* 6. Make prev_node as previous of new_node */
+    new_node->prev = prev_node; 
+  
+    /* 7. Change previous of new_node's next node */
+    if (new_node->next != NULL) 
+        new_node->next->prev = new_node; 
+} 
+  
+/* Given a reference (pointer to pointer) to the head 
+   of a DLL and an int, appends a new node at the end  */
+void append(struct Node** head_ref, int new_data) 
+{ 
+    /* 1. allocate node */
+    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); 
+  
+    struct Node* last = *head_ref; /* used in step 5*/
+  
+    /* 2. put in the data  */
+    new_node->data = new_data; 
+  
+    /* 3. This new node is going to be the last node, so 
+          make next of it as NULL*/
+    new_node->next = NULL; 
+  
+    /* 4. If the Linked List is empty, then make the new 
+          node as head */
+    if (*head_ref == NULL) { 
+        new_node->prev = NULL; 
+        *head_ref = new_node; 
+        return; 
+    } 
+  
+    /* 5. Else traverse till the last node */
+    while (last->next != NULL) 
+        last = last->next; 
+  
+    /* 6. Change the next of last node */
+    last->next = new_node; 
+  
+    /* 7. Make last node as previous of new node */
+    new_node->prev = last; 
+  
+    return; 
+} 
+  
+// This function prints contents of linked list starting from the given node 
+void printList(struct Node* node) 
+{ 
+    struct Node* last; 
+    printf("\nTraversal in forward direction \n"); 
+    while (node != NULL) { 
+        printf(" %d ", node->data); 
+        last = node; 
+        node = node->next; 
+    } 
+  
+    printf("\nTraversal in reverse direction \n"); 
+    while (last != NULL) { 
+        printf(" %d ", last->data); 
+        last = last->prev; 
+    } 
+} 
+  
+/* Drier program to test above functions*/
+int main() 
+{ 
+    /* Start with the empty list */
+    struct Node* head = NULL; 
+  
+    // Insert 6.  So linked list becomes 6->NULL 
+    append(&head, 6); 
+  
+    // Insert 7 at the beginning. So linked list becomes 7->6->NULL 
+    push(&head, 7); 
+  
+    // Insert 1 at the beginning. So linked list becomes 1->7->6->NULL 
+    push(&head, 1); 
+  
+    // Insert 4 at the end. So linked list becomes 1->7->6->4->NULL 
+    append(&head, 4); 
+  
+    // Insert 8, after 7. So linked list becomes 1->7->8->6->4->NULL 
+    insertAfter(head->next, 8); 
+  
+    printf("Created DLL is: "); 
+    printList(head); 
+  
+    getchar(); 
+    return 0; 
+}