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
        // return result
        if(head == null){
            return null;
        }
        // node is not null
        // create new node
        ListNode node = new ListNode(head.val);
        // where next of next is not null
        while(head.next != null){
            // foreach next node, create new node
            head = head.next;
            ListNode temp = new ListNode(head.val);
            temp.next = node;
            node = temp;
        }
        return node;
    }
}