19. Remove Nth Node From End of List | LeetCode Solution

 19. Remove Nth Node From End of List | LeetCode Solution

Given the head of a linked list, remove the nth node from the end of the list and return its head.

 

Example 1:

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

Example 2:

Input: head = [1], n = 1
Output: []

Example 3:

Input: head = [1,2], n = 1
Output: [1]

 

Constraints:

• The number of nodes in the list is sz.
• 1 <= sz <= 30
• 0 <= Node.val <= 100
• 1 <= n <= sz

/**

 * Definition for singly-linked list.

 * struct ListNode {

 *     int val;

 *     ListNode *next;

 *     ListNode() : val(0), next(nullptr) {}

 *     ListNode(int x) : val(x), next(nullptr) {}

 *     ListNode(int x, ListNode *next) : val(x), next(next) {}

 * };

 */

class Solution {

public:

    ListNode* removeNthFromEnd(ListNode* head, int n) {

        if((n==1 && head==NULL) || (head->next==NULL && n==1))return NULL;

        

        ListNode* fast=head;

        ListNode* slow=head;

        

        while(n--){

            fast=fast->next;

        }

        if(fast==NULL)return head->next;

        

        while(fast->next!=NULL){

            fast=fast->next;

            slow=slow->next;

        }

        slow->next=slow->next->next;

        return head;

        

    }

};