Different ways to insert in Singly Linked List

Author: sudesh1611

Data Structures/SinglyLinkedList/Insertion.c

@@ -0,0 +1,121 @@
+// A complete working C program to demonstrate all insertion methods
+// on Linked List
+#include <stdio.h>
+#include <stdlib.h>
+
+// A linked list node
+struct Node
+{
+  int data;
+  struct Node *next;
+};
+
+/* 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 */
+    new_node->next = (*head_ref);
+
+    /* 4. move the head to point to the new node */
+    (*head_ref)    = new_node;
+}
+
+/* Given a node prev_node, insert a new node after the given
+   prev_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. move the next of prev_node as new_node */
+    prev_node->next = new_node;
+}
+
+/* Given a reference (pointer to pointer) to the head
+   of a list 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)
+    {
+       *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;
+    return;
+}
+
+// This function prints contents of linked list starting from head
+void printList(struct Node *node)
+{
+  while (node != NULL)
+  {
+     printf(" %d ", node->data);
+     node = node->next;
+  }
+}
+
+/* Driver 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("\n Created Linked list is: ");
+  printList(head);
+
+  return 0;
+}