LeetCode19. Remove Nth Node From End of List

文章目录

• • 一、题目
  • 二、题解

一、题目

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

Follow up: Could you do this in one pass?

二、题解

/**
 * 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) {
        ListNode* dummyHead = new ListNode(0);
        dummyHead->next = head;
        ListNode* fast = dummyHead;
        ListNode* slow = dummyHead;
        n++;
        while(n-- && fast != nullptr){
            fast = fast->next;
        }
        while(fast != nullptr){
            fast = fast->next;
            slow = slow->next;
        }
        slow->next = slow->next->next;
        return dummyHead->next;
    }
};