Javascript Program For Inserting A Node After The N-th Node From The End
Insert a node x after the nth node from the end in the given singly linked list. It is guaranteed that the list contains the nth node from the end. Also 1 <= n.
Examples:
Input : list: 1->3->4->5 n = 4, x = 2 Output : 1->2->3->4->5 4th node from the end is 1 and insertion has been done after this node. Input : list: 10->8->3->12->5->18 n = 2, x = 11 Output : 10->8->3->12->5->11->18
Method 1 (Using length of the list):
Find the length of the linked list, i.e, the number of nodes in the list. Let it be len. Now traverse the list from the 1st node upto the (len-n+1)th node from the beginning and insert the new node after this node. This method requires two traversals of the list.
Javascript
<script> // JavaScript implementation to // insert a node after // the n-th node from the end // structure of a node class Node { constructor() { this .data = 0; this .next = null ; } } // function to get a new node function getNode(data) { // allocate memory for the node var newNode = new Node(); // put in the data newNode.data = data; newNode.next = null ; return newNode; } // function to insert a node after the // nth node from the end function insertAfterNthNode(head , n , x) { // if list is empty if (head == null ) return ; // get a new node for the value 'x' var newNode = getNode(x); var ptr = head; var len = 0, i; // find length of the list, i.e, the // number of nodes in the list while (ptr != null ) { len++; ptr = ptr.next; } // traverse up to the nth node from the end ptr = head; for (i = 1; i <= (len - n); i++) ptr = ptr.next; // insert the 'newNode' by making the // necessary adjustment in the links newNode.next = ptr.next; ptr.next = newNode; } // function to print the list function printList(head) { while (head != null ) { document.write(head.data + " " ); head = head.next; } } // Driver code // Creating list 1->3->4->5 var head = getNode(1); head.next = getNode(3); head.next.next = getNode(4); head.next.next.next = getNode(5); var n = 4, x = 2; document.write( "Original Linked List: " ); printList(head); insertAfterNthNode(head, n, x); document.write(); document.write( "<br/>Linked List After Insertion: " ); printList(head); // This code contributed by gauravrajput1 </script> |
Output:
Original Linked List: 1 3 4 5 Linked List After Insertion: 1 2 3 4 5
Time Complexity: O(n), where n is the number of nodes in the list.
Auxiliary space: O(1) because using constant variables
Method 2 (Single traversal):
This method uses two pointers, one is slow_ptr and the other is fast_ptr. First move the fast_ptr up to the nth node from the beginning. Make the slow_ptr point to the 1st node of the list. Now, simultaneously move both the pointers until fast_ptr points to the last node. At this point the slow_ptr will be pointing to the nth node from the end. Insert the new node after this node. This method requires single traversal of the list.
Javascript
<script> // JavaScript implementation to // insert a node after the // nth node from the end // structure of a node class Node { constructor() { this .data = 0; this .next = null ; } } // function to get a new node function getNode(data) { // allocate memory for the node var newNode = new Node(); // put in the data newNode.data = data; newNode.next = null ; return newNode; } // function to insert a node after // the nth node from the end function insertAfterNthNode(head, n, x) { // if list is empty if (head == null ) return ; // get a new node for the value 'x' var newNode = getNode(x); // Initializing the slow // and fast pointers var slow_ptr = head; var fast_ptr = head; // move 'fast_ptr' to point to the // nth node from the beginning for ( var i = 1; i <= n - 1; i++) fast_ptr = fast_ptr.next; // iterate until 'fast_ptr' points // to the last node while (fast_ptr.next != null ) { // move both the pointers to the // respective next nodes slow_ptr = slow_ptr.next; fast_ptr = fast_ptr.next; } // insert the 'newNode' by making the // necessary adjustment in the links newNode.next = slow_ptr.next; slow_ptr.next = newNode; } // function to print the list function printList(head) { while (head != null ) { document.write(head.data + " " ); head = head.next; } } // Driver code // Creating list 1->3->4->5 var head = getNode(1); head.next = getNode(3); head.next.next = getNode(4); head.next.next.next = getNode(5); var n = 4, x = 2; document.write( "Original Linked List: " ); printList(head); insertAfterNthNode(head, n, x); document.write( "<br>" ); document.write( "Linked List After Insertion:" ); printList(head); </script> |
Output:
Original Linked List: 1 3 4 5 Linked List After Insertion: 1 2 3 4 5
Time Complexity: O(n), where n is the number of nodes in the list.
Space Complexity: O(1) using constant space
Please refer complete article on Insert a node after the n-th node from the end for more details!
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