remove-nth-node-from-end-of-list

题目描述

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) {
        if(n<=0) return NULL;
        if(!head) return head;
        
        ListNode *dummy = new ListNode(-1);
        dummy->next = head;
        
        ListNode *fast = dummy;
        ListNode *slow = dummy;
        
        while(n>0){
            fast = fast->next;
            --n;
        }
        
        if(!fast)
            return NULL;
        
        while(fast->next){
            fast = fast->next;
            slow = slow->next;
        }
        
        slow->next = slow->next->next;
        return dummy->next;
    }
};