LeetCode (Remove Nth Node From End of List)

Problem:

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.

Solution:

/** * 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) {        int length = 0;        ListNode  l(0), *p = &l;        l.next = head;        while(head != NULL){            length++;            head = head->next;        }        for (int i = 1; i <= length; i++){            if (i !=(length - n + 1))                p = p->next;            else                 p->next = p->next->next;        }        return l.next;    }};