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;
        
    }
};

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