题目描述

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.

样例

Example:

Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:

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

算法1

(暴力枚举) $O(n)$

层序遍历整个数，每层先遍历右子树，且将每层最右的节点放入数组。

时间复杂度

每个节点走一遍，O（n）
递归调用栈，空间复杂度O（n）

参考文献

C++ 代码

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

算法2

(暴力枚举) $O(n^2)$

blablabla

时间复杂度

参考文献

C++ 代码

blablabla