题解 | 反转链表

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode ReverseList (ListNode head) {
        // write code here
        //先判断是否为空
        if(head == null){
            return null;
        }
	  //三指针模型
        ListNode prev = null;
        ListNode curr = head;
        ListNode nex = head.next;
        while(curr != null){
            nex = curr.next;
            curr.next = prev;
            prev = curr;
            curr = nex;
        }
        return prev;
    }
}