Table of Contents

## Problem Statement

The Remove Nth Node From End of List Leetcode Solution – states that you are given the head of a linked list and you need to remove the nth node from the end of this list.

After deleting this node, return the head of the modified list.

## Example:

Input: head = [1,2,3,4,5], n = 2

Output: [1,2,3,5]

Explanation:

- We have to remove the second node from the end of the list, the node with value 4.
- After deleting this node, we have the modified list containing all the elements as [1,2,3,5].

Input: head = [1], n = 1

Output: []

Explanation:

- We need to remove the end node of the list.
- After removing the node, we have an empty list.

## Approach

### Idea:

- The main idea to solve this problem is to use
**three variables**that store the node’s addresses.*curr*= It will store the current node’s address used to iterate in the linked list.*start*= It will store the node’s address that will be deleted (nth node from the end of the list).*prev*= It will store the previous node’s address of the node’s start.

- Note that, the distance between the deleting node and head of the linked list is
**m-n**and the distance between deleting node and end of the linked list is n, where m = length of linked list. - The above observation suggests that
**start the curr variable from the head of the linked list**and**decrement n each time as we move forward in the linked list**. As soon as we have**n as a non-positive value**, initialize the start variable with the address of the head of the linked list and increment the start variable as well as the prev variable each time when n is non-positive. - Step 3 works efficiently since whatever the distance curr variable covers after n becomes non-positive, will be equal to the distance covered by the start variable from the head of the linked list which is
**m-n**. Hence, we’ll end up with the nth node from the end’s address stored in the start variable. **Delete the node contained in the start variable**, by assigning prev next node address as the start next address.- Check code for better understanding.

## Code

### Remove Nth Node From End of List Leetcode C++ Solution:

class Solution { public: ListNode* removeNthFromEnd(ListNode* head, int n) { ListNode *prev = nullptr,*curr = head,*start = nullptr; while(curr!=nullptr){ n--; curr = curr->next; if(n<=0){ if(start==nullptr){ start = head; } else{ prev = start; start = start->next; } } } if(prev==nullptr){ return start->next; } prev->next = start->next; return head; } };

### Remove Nth Node From End of List Leetcode Java Solution:

class Solution { public ListNode removeNthFromEnd(ListNode head, int n) { ListNode curr = head; ListNode prev = null; ListNode start = null; while(curr!=null){ n = n - 1; curr = curr.next; if(n<=0){ if(start==null){ start = head; } else{ prev = start; start = start.next; } } } if(prev==null){ return start.next; } prev.next = start.next; return head; } }

## Complexity Analysis for Remove Nth Node From End of List Leetcode Solution

### Time Complexity

The time complexity of the above code is **O(N), **where N = length of the linked list since we’re iterating for the entire linked list one time.

### Space Complexity

The space complexity of the above code **O(1)** since we’re using constant extra space.