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
        if(head == null) return head;
        List<ListNode> nodeList = new ArrayList<>();
        nodeList.add(head);
        ListNode nextTemp = head;
        while(true){
            ListNode next = nextTemp.next;
            if(next == null) break;
            nodeList.add(next);
            nextTemp = next;
        }

        for(int i=nodeList.size()-1; i>0; i--){
            ListNode target = nodeList.get(i);
            ListNode target1 = nodeList.get(i-1);
            target1.next = null;
            target.next = nodeList.get(i-1);
        }
        
        return nodeList.get(nodeList.size()-1);
    }
}