Find Largest Value in Each Tree Row

给一个二叉树, 找每层最大的值. 直接层序扫描.

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 size = q.size();
            int max = Integer.MIN_VALUE;
            for(int i = 0; i < size; i++) {
                TreeNode node = q.poll();
                max = Math.max(max, node.val);
                if(node.left != null)
                    q.offer(node.left);
                if(node.right != null)
                    q.offer(node.right);
            }
            res.add(max);
        }
        return res;
    }
}