19. Remove Nth Node From End of List(Leetcode每日一题-2020.10.18)

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Problem

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

Constraints:

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

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

Example1

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

Example2

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

Example3

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

Solution

双指针

/*** Definition for singly-linked list.* struct ListNode {*     int val;*     ListNode *next;*     ListNode(int x) : val(x), next(NULL) {}* };*/
class Solution {
public:ListNode* removeNthFromEnd(ListNode* head, int n) {if(!head)return NULL;ListNode *fast = head;while(n){fast = fast->next;--n;}ListNode dummy;dummy.next = head;ListNode *slow = head;ListNode *prev = &dummy;while(fast){fast = fast->next;slow = slow->next;prev = prev->next;}prev->next = slow->next;return dummy.next;}
};

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