515.find-largest-value-in-each-tree-row.java

import java.util.Queue;

import javax.swing.tree.TreeNode;

/*
 * @lc app=leetcode id=515 lang=java
 *
 * [515] Find Largest Value in Each Tree Row
 */

// @lc code=start
/**
 * 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;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        int tempMax = Integer.MIN_VALUE;

        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode curr = queue.poll();
                tempMax = Math.max(tempMax, curr.val);

                if (curr.left != null) {
                    queue.add(curr.left);
                }
                if (curr.right != null) {
                    queue.add(curr.right);
                }
            }
            result.add(tempMax);
            tempMax = Integer.MIN_VALUE;
        }
        return result;
    }
}
// @lc code=end