Remove Nth Node From End of List 删除链表倒数第N个节点

Remove Nth Node From End of List

Given a linked list, remove the nth

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 *p=head,*q=head;
        int z=n;
        while(z--)
        {
            p=p->next;
        }
        if(p==NULL)
        {
            return head->next;
        }
        
        while(p->next)
        {
            q=q->next;
            p=p->next;
        }
       
        q->next=q->next->next;
        return head;
    }
};