题目描述

不分行从上往下打印二叉树
java实现

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    //层序遍历-->队列迭代法
    public List<Integer> printFromTopToBottom(TreeNode root) {
        //定义结果数组
        List<Integer> result = new ArrayList<>();
        if(root==null) return result;

        //定义队列结构
        Queue<TreeNode> que = new LinkedList<>();
        que.offer(root);

        //遍历队列 打印每一层节点的值
        while(!que.isEmpty()) {
            int size = que.size();
            for(int i = 0; i < size; i++) {
                TreeNode node = que.poll();
                result.add(node.val);

                if(node.left != null) que.offer(node.left);
                if(node.right != null) que.offer(node.right);
            }
        }
        return result;
    }
}