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。