leetcode：Remove Nth Node From End of List 【Java】

一、问题描述

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.
二、问题分析

使用两个指针，使其中一个指针比另一个多走n步。

三、算法代码

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode cur = head;
        for(int i = 0; i < n; i++){
            cur = cur.next;
        }
        
        if(cur == null){
            head = head.next;
            return head;
        }
        
        ListNode pre = head;
        while(cur.next != null){
            cur = cur.next;
            pre = pre.next;
        }
        ListNode target = pre.next;
        pre.next = target.next;
        return head;
    }
}