LeetCode: 199. Binary Tree Right Side View

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.

Example:

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

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

解题思路 —— 递归分治

前序遍历二叉树节点， 当某一层出现新的节点后，替换掉当前在该层保存的节点。

AC 代码

/**
 * 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 {
     void rightSideView(TreeNode* root, vector<int>& record, int depth = 0)
     {
         if(root == nullptr) return;

         if(depth >= record.size()) record.push_back(root->val);
         else record[depth] = root->val;

         rightSideView(root->left, record, depth+1);
         rightSideView(root->right, record, depth+1);
     }
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int> ans;
        rightSideView(root, ans);

        return ans;
    }
};