InsertNodeDoublyLinkedList.cpp

LinkedList/InsertNodeDoublyLinkedList.cpp

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+// A simple C++ program to insert a node at user-defined position in a Doubly linked list
+
+#include<iostream>
+using namespace std;
+
+class node
+{
+    public:
+
+    int data;
+    node *next, *prev; 
+    // next is a pointer that points to the next node of the DLL(doubly linked list).
+    // prev is a pointer that points to the previous node of the DLL.
+};
+
+int main()
+{
+    int i, n, key, pos;
+
+    node *p, *q, *head, *tail, *temp, *new_node;
+
+    // q is the DLL node.
+    // p is a temporary variable used to iterate over the DLL q.
+    // head is pointer that points to the first node of the DLL.
+    // tail is pointer that points to the last node of the 
+    // temp is used to store the previous node
+    // new_node is the node which is inserted in the list.
+
+    // taking user input for number of nodes.
+    cout<<"Enter number of nodes: ";
+    cin>>n;
+
+    q = new node; // creating a node using new keyword.
+
+    cout<<"Enter value of 1st  node: ";
+    cin>>q->data; // assign data to the 1st node.
+
+    q->next = NULL;
+    q->prev = NULL;
+    head = q; // head points to the first node of the DLL
+    tail = q; // tail points to the last node of the DLL
+
+    for(i = 1; i < n; i++)
+    {
+        q = new node;
+
+        cout<<"Enter value of next node: ";
+        cin>>q->data; // user input for next node data.
+
+        q->next = NULL;
+        q->prev = tail;
+        tail->next = q;
+        tail = tail->next;   
+
+    // every interation creates a node and data is assigned to it.
+}
+tail->next = NULL; 
+
+p = head;
+
+// printing the doubly linked list.
+cout<<"\nDoubly linked list node data: ";
+
+while(p != NULL)
+{
+    cout<<p->data<<" ";
+    p = p->next;
+}
+
+start:
+// Doubly Linked List nodes are indexed on Zero based indexing.
+cout<<"\nEnter data to insert node in the doubly linked list: ";
+cin>>key;      // Data for the new node.
+cout<<"\nEnter index position to insert node: ";
+cin>>pos;     // Position to insert the newly created node in list.
+
+if(pos == 0)  // this block of code creates and insert the newly created node in the begining.
+{
+    p = head;
+    new_node = new node;
+    new_node->data = key;
+    new_node->prev = NULL;
+    new_node->next = p;
+    p->prev = new_node;
+    head = new_node;
+}
+else if(pos == n) // this block of code creates and insert the newly created node at the end of the list.
+{
+    p = tail;
+    new_node = new node;
+    new_node->data = key;
+    new_node->next = NULL;
+    new_node->prev = p;
+    p->next = new_node;
+    tail = new_node;
+}
+else if(pos > 0 && pos <= n-1) // this block of code creates and insert node from 2nd position to n-1th position.
+{
+    p = head;
+    for(i = 0; i < pos; i++) 
+    {
+        temp = p;
+        p = p->next;
+    }
+
+    // temp stores the node, previous to the node which is at index 'pos'.
+
+    new_node = new node;
+    new_node->data = key;
+    new_node->next = p;
+    new_node->prev = temp;
+    temp->next = new_node;
+    p->prev = new_node;
+}
+else // if pos < 0 || pos > n. Then node cannot be inserted.
+{
+    cout<<"Entered an invalid index. Try again!";
+    goto start; // Again enter the position to insert.
+}
+
+p = head;
+
+//printing the list after inserting the node.
+cout<<"\nDoubly linked list node data after insertion: ";
+while(p != NULL)
+{
+    cout<<p->data<<" ";
+    p = p->next;
+}
+
+return 0;
+
+}