3. 从尾到头打印链表

最新推荐文章于 2024-10-31 20:36:13 发布

原创最新推荐文章于 2024-10-31 20:36:13 发布 · 166 阅读

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文章目录

1. 反转链表
2. 反转集合
3. 递归

1. 反转链表

/**
 * @Classname Solution
 * @Description 从尾到头打印链表
 * @Date 2019/12/17 15:24
 * @Created by Cheng
 */
public class Solution {   
    public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ArrayList<Integer> ret = new ArrayList<>();
        if (listNode == null) return ret;
        listNode = reverseLinkedList(listNode);
        while (listNode != null) {
            ret.add(listNode.val);
            listNode = listNode.next;
        }
        return ret;
    }

    private ListNode reverseLinkedList(ListNode node) {
        ListNode dummyHead = new ListNode(0);
        ListNode cur = dummyHead;
        ListNode next = null;
        while (node != null) {
            next = node.next;
            node.next = dummyHead.next;
            dummyHead.next = node;
            node = next;
        }
        return dummyHead.next;
    }
}

2. 反转集合

/**
 * @Classname Solution
 * @Description 从尾到头打印链表
 * @Date 2019/12/17 15:24
 * @Created by Cheng
 */
public class Solution {
    public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ArrayList<Integer> ret = new ArrayList<>();
        if (listNode == null) return ret;
        while (listNode != null) {
            ret.add(listNode.val);
            listNode = listNode.next;
        }
        Collections.reverse(ret);
        return ret;
    }
}

3. 递归

/**
 * @Classname Solution
 * @Description 从尾到头打印链表
 * @Date 2019/12/17 15:24
 * @Created by Cheng
 */
public class Solution {
    public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ArrayList<Integer> ret = new ArrayList<>();
        if (listNode == null) return ret;
        recursion(ret, listNode);
        return ret;
    }

    private void recursion(ArrayList<Integer> ret, ListNode listNode) {
        if (listNode.next != null)
            recursion(ret, listNode.next);
        ret.add(listNode.val);
    }
}