leetcode [#206]

目录

• 1. 题目
• 2. 解决方案
• 3. 注意事项

题目

Reverse a singly linked list.

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解决方案

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode reverseList(ListNode head) {
        if(head == null || head.next == null) return head;
        ArrayList<Integer> valList = new ArrayList<Integer>();

        ListNode p = head;
        while (p != null){
            valList.add(p.val);
            p = p.next;
        }
        ListNode newHead = new ListNode(0);
        ListNode q = newHead;

        for(int k = valList.size()-1; k >= 0; k--){
            q.val = valList.get(k);
            if(k == 0){
                q.next = null;
            } else {
                q.next = new ListNode(0);
            }
            q = q.next;
        }
        return newHead;
    }
}

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注意事项

1. 翻转链表。获取所有元素，倒序构建新链表。