Force buckle 515 Find the maximum value in each tree row

subject

Given the root node of a binary tree root , Please find the maximum value of each layer in the binary tree .

Example

Input : root = [1,3,2,5,3,null,9]
Output : [1,3,9]

Input : root = [1,2,3]
Output : [1,3]

source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/find-largest-value-in-each-tree-row
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Method 1： queue

Java Realization

class Solution {
    
    public List<Integer> largestValues(TreeNode root) {
    
        List<Integer> res = new ArrayList<>();
        if (root == null) return res;
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);

        while (!q.isEmpty()) {
    
            int sz = q.size();
            int max = Integer.MIN_VALUE;
            for (int i = 0; i < sz; i++) {
    
                TreeNode cur = q.poll();
                max = cur.val > max ? cur.val : max;
                if (cur.left != null) q.offer(cur.left);
                if (cur.right != null) q.offer(cur.right);
            }
            res.add(max);
        }
        return res;
    }
}