[LeetCode] Remove Nth Node From End of List

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 (!head->next) return NULL;
        ListNode *ans = head, *cur = head;
        for (int i = 0; i < n; i++) cur = cur->next;
        if (!cur) return head->next;
        while (cur->next)
        {
            cur = cur->next;
            ans = ans->next;
        }
        ans->next = ans->next->next;
        return head;
    }
};