力扣-199.二叉树的右视图

题目链接

199.二叉树的右视图

class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> res = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        if (root == null)
            return res;
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode temp = queue.poll();
                if (i == size - 1) {
                    res.add(temp.val);
                }
                if (temp.left != null)
                    queue.offer(temp.left);
                if (temp.right != null)
                    queue.offer(temp.right);
            }
        }
        return res;
    }
}

小结：秒了！树的题目变化不多，想到层序遍历就容易了。