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题目

给定一个二叉树的 根节点 root，想象自己站在它的右侧，按照从顶部到底部的顺序，返回从右侧所能看到的节点值。

示例 1:

输入: [1,2,3,null,5,null,4]
输出: [1,3,4]

解

class Solution {public List<Integer> rightSideView(TreeNode root) {return bfs(root);}public List<Integer> bfs(TreeNode root) {List<Integer> res = new ArrayList<>();if (root == null) {return res;}LinkedList<TreeNode> queue1 = new LinkedList<>();LinkedList<TreeNode> queue2 = new LinkedList<>();queue1.offer(root);while (!queue1.isEmpty()) {TreeNode poll = queue1.poll();if (poll.left != null) {queue2.add(poll.left);}if (poll.right != null) {queue2.add(poll.right);}if (queue1.isEmpty()) {res.add(poll.val);queue1 = queue2;queue2 = new LinkedList<>();}}return res;}
}