【LeetCode】515.在每个树行中找最大值

题目链接
给定一棵二叉树的根节点 root ，请找出该二叉树中每一层的最大值。

示例1：

输入: root = [1,3,2,5,3,null,9]
输出: [1,3,9]

示例2：

输入: root = [1,2,3]
输出: [1,3]

提示：

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

/**
* 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) {
        List<Integer> result = new ArrayList<>();

        if (root == null) {
            return result;
        }

        Deque<TreeNode> deque = new LinkedList<>();
        deque.offer(root);

        while (!deque.isEmpty()) {
            List<Integer> temp = new ArrayList<>();
            int size = deque.size();

            int max = deque.peek().val;
            for (int i = 0; i < size; i++) {
                TreeNode node = deque.poll();
                if (node.val > max) {
                    max = node.val;
                }
                if (node.left != null) {
                    deque.add(node.left);
                }
                if (node.right != null) {
                    deque.add(node.right);
                }
            }
            result.add(max);
        }
        return result;
    }
}