515. Find Largest Value in Each Tree Row

Medium
考Binary Tree Level Order Traversal,简单秒.

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