LeetCode刷题（C++）——Remove Nth Node From End of List（Medium）

Given a linked list, remove the nth 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) {        if (head == NULL)return NULL;ListNode phead(-1);phead.next = head;ListNode* fast = head;ListNode* slow = head;ListNode* pre = &phead;for (int i = 0; i < n;i++)fast = fast->next;while (fast!=NULL){fast = fast->next;slow = slow->next;pre = pre->next;}pre->next = slow->next;free(slow);return phead.next;    }};