leetcode Remove Nth Node From End of List

原题链接：https://leetcode.com/problems/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;
};