Added insertion program for linked lists.

Program's_Contributed_By_Contributors/C++_Programs/Linked List/Insertion.cpp

@@ -0,0 +1,132 @@
+// A complete working C++ program to demonstrate
+//  all insertion methods on Linked List
+#include <bits/stdc++.h>
+using namespace std;
+
+// A linked list node
+class Node
+{
+    public:
+    int data;
+    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(Node** head_ref, int new_data)
+{
+    /* 1. allocate node */
+    Node* new_node = new 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(Node* prev_node, int new_data)
+{
+    /*1. check if the given prev_node is NULL */
+    if (prev_node == NULL)
+    {
+        cout<<"The given previous node cannot be NULL";
+        return;
+    }
+
+    /* 2. allocate new node */
+    Node* new_node = new 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(Node** head_ref, int new_data)
+{
+    /* 1. allocate node */
+    Node* new_node = new Node();
+
+    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(Node *node)
+{
+    while (node != NULL)
+    {
+        cout<<" "<<node->data;
+        node = node->next;
+    }
+}
+
+/* Driver code*/
+int main()
+{
+    /* Start with the empty list */
+    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);
+
+    cout<<"Created Linked list is: ";
+    printList(head);
+
+    return 0;
+}