题目描述

LeetCode 剑指 Offer II 044. 二叉树每层的最大值
提示：


    二叉树的节点个数的范围是 [0,104]
    -231 <= Node.val <= 231 - 1

一、解题关键词

广度优先

二、解题报告

1.思路分析

2.时间复杂度

3.代码示例

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Integer> largestValues(TreeNode root) {
        //BFS 找到当前层最大值
        List<Integer> result = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        if(root != null) queue.add(root);
        while(!queue.isEmpty()){
            int num = Integer.MIN_VALUE;
            int lg = queue.size();
            for(int i = 0; i < lg;i++){
                TreeNode node = queue.poll();
                num = Math.max(num,node.val);
                if(node.left != null){
                    queue.add(node.left);
                }
                if(node.right != null){
                    queue.add(node.right);
                }
                
            } 
            result.add(num);           
        }

        return result;
    }
}