【数据结构】算法 Print Binary Tree Top to Bottom 从上到下打印二叉树

目录

• Print Binary Tree Top to Bottom 从上到下打印二叉树
• 思路
• Tag

Print Binary Tree Top to Bottom 从上到下打印二叉树

从上到下按层打印二叉树，一层从左到右打印。

思路

使用queue完成对树的层序遍历

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    
    
    public List<List<Integer>> levelOrder(TreeNode root) {
       List<List<Integer>> ans = new ArrayList<>();
        if(root==null){
            return ans;
        }
        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);
        while(!queue.isEmpty()){
            ArrayList<Integer> integers = new ArrayList<>();
            int length = queue.size();
            for (int i = 0; i < length ; i++) {
                TreeNode node = queue.poll();
                integers.add(node.val);
                if(node.left!=null){
                    queue.offer(node.left);
                }
                if(node.right!=null){
                    queue.offer(node.right);
                }
            }
            ans.add(integers);
        }
        return ans;
    }
}

Tag

tree