Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Example:

Input: [1,2,3,null,5,null,4]Output: [1, 3, 4]Explanation:   1            <--- /   \2     3         <--- \     \  5     4       <---

难度： medium

题目： 给定二叉树，想像一下你站在树的右边，返回能看到的所有结点，结点从上到下输出。

思路：层次遍历，ＢＦＳ

Runtime: 1 ms, faster than 79.74% of Java online submissions for Binary Tree Right Side View.

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