leetcode114. 二叉树展开为链表（java）

问题描述：
给定一个二叉树，原地将它展开为链表。

例如：给定二叉树

eg:
1
/
2 5
/ \
3 4 6
将其展开为：

1

2

3

4

5

6
上代码，拿去即可运行：

package com.onlyqi.upup01.tree;

import com.onlyqi.upup01.leetcode.TreeNode;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Objects;

public class Test03 {
    
    
    public static void main(String[] args) {
    
    
        TreeNode treeNode1 = new TreeNode(1);
        TreeNode treeNode2 = new TreeNode(2);
        TreeNode treeNode3 = new TreeNode(3);
        TreeNode treeNode4 = new TreeNode(4);
        TreeNode treeNode5 = new TreeNode(5);
        TreeNode treeNode6 = new TreeNode(6);
        treeNode5.setRightNode(treeNode6);
        treeNode2.setLefTreeNode(treeNode3);
        treeNode2.setRightNode(treeNode4);
        treeNode1.setLefTreeNode(treeNode2);
        treeNode1.setRightNode(treeNode5);
        List<Integer>aa=new ArrayList<>();
        aa.add(treeNode1.getValue());
        aa.addAll(levelOrderTraversal(treeNode1.getLefTreeNode()));
        aa.addAll( levelOrderTraversal(treeNode5));
        aa.stream().forEach(s-> System.out.println(s));
    }

    public static List<Integer> levelOrderTraversal(TreeNode treeNode) {
    
    
        List<Integer>valueList=new ArrayList<>();
        LinkedList<TreeNode> q = new LinkedList<>();   // 创建队列
        TreeNode node=new TreeNode();

        q.push(treeNode);  // treeNode 入队
        while (!q.isEmpty()) {
    
    
            node = q.getFirst();  // 访问队首元素
            q.pop();  // 出队
            valueList.add(node.getValue());
            if (node.getLefTreeNode() != null) {
    
    // 如果存在左儿子结点
                q.addLast(node.getLefTreeNode());  // 入队
            }
            if (node.getRightNode() != null) {
    
    
                q.addLast(node.getRightNode());
            }
        }
        return valueList;
    }





}

我要刷100道算法题，第82道