LeetCode 199: 二叉树的右视图

[guodongxiaren]

https://leetcode-cn.com/problems/binary-tree-right-side-view

给定一棵二叉树，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:

输入: [1,2,3,null,5,null,4] 输出: [1, 3, 4] 解释:

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

[guodongxiaren]

亚马逊问过我~

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int> res;
        // level from 0
        rightSide(root, 0, res);
        return res;
    }
    void rightSide(TreeNode* root, int level, vector<int>& res) {
        if (!root) {
            return;
        }
        if ((int)res.size() - 1 < level) {
            res.push_back(root->val);
        }
        rightSide(root->right, level+1, res);
        rightSide(root->left, level+1, res);
    }
};