From 97bbf7038aa6a4c7cf7932f1db931ea76437d194 Mon Sep 17 00:00:00 2001
From: CannanDashiell <53655257+CannanDashiell@users.noreply.github.com>
Date: Fri, 2 Oct 2020 19:00:26 +0530
Subject: [PATCH] Create DeleteNodeDoublyLinkedList.cpp

---
 LinkedList/DeleteNodeDoublyLinkedList.cpp | 121 ++++++++++++++++++++++
 1 file changed, 121 insertions(+)
 create mode 100644 LinkedList/DeleteNodeDoublyLinkedList.cpp

diff --git a/LinkedList/DeleteNodeDoublyLinkedList.cpp b/LinkedList/DeleteNodeDoublyLinkedList.cpp
new file mode 100644
index 0000000..50fc921
--- /dev/null
+++ b/LinkedList/DeleteNodeDoublyLinkedList.cpp
@@ -0,0 +1,121 @@
+// A simple C++ program for deleting a node from 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;
+    
+    node *p, *q, *head, *tail, *temp;
+    
+    // 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
+    
+    // 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:
+// Linked List nodes are indexed on Zero based indexing.
+cout<<"\nEnter an index position to delete node from the doubly linked list: ";
+cin>>key;
+
+if(key == 0)  // this block of code points head to the node which is next to 1st node i.e. 2nd node.
+{
+    p = head;
+    p = p->next;
+    head = p;
+    p->prev = NULL;
+}
+else if(key == n-1) // this block of code points tail to the 2nd last node of the list.
+{
+    p = tail->prev;
+    tail = p;
+    p->next = NULL;
+    tail->next = NULL;
+}
+else if(key > 0 && key < n-1)// this block manages deletion of the node for other index value 0 to n-1.
+{
+    p = head;
+    for(i = 0; i < key; i++) 
+    {
+        temp = p;
+        p = p->next;
+    }
+
+    // temp stores the node, previous to the node which is at index 'key'.
+    p = p->next;
+    temp->next = p;
+    p->prev = temp;
+}
+else // if key value is greater than, equal to n or less than 0.
+{
+    cout<<"Entered an invalid index. Try again!";
+    goto start;
+}
+
+p = head;
+
+//printing the list after deletion.
+cout<<"\nDoubly linked list node data after deletion: ";
+while(p != NULL)
+{
+    cout<<p->data<<" ";
+    p = p->next;
+}
+
+return 0;
+
+}