leetcode Remove Nth Node From End of List

题目连接

https://leetcode.com/problems/remove-nth-node-from-end-of-list/

Remove Nth Node From End of List

Description

Given a linked list, remove the $n^{th}$ node from the end of list and return its head.

For example,

Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.
Note:
Given n will always be valid.
Try to do this in one pass.

/**
 * 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) {
		tot = 0;
		if (!head) return head;
		ListNode *p = head;
		for (; p; p = p->next) tot++;
		if (n > tot) return head;
		p = head;
		int cur = 1;
		if (tot == n) {
			head = head->next;
			delete p;
		} else {
			while (p) {
				if (cur++ == tot - n) break;
				p = p->next;
			}
			ListNode *ret = p->next;
			p->next = ret ? ret->next : NULL;
			delete ret;
		}
		return head;
	}
private:
	int tot;
};