LeetCode - Binary Tree Right Side View

Binary Tree Right Side View

2015.4.17 06:04

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.

For example:
Given the following binary tree,

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.

For example:
Given the following binary tree,
   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---
You should return [1, 3, 4].

You should return [1, 3, 4].

Solution:

　　Recursion can provide you with a short solution. So make it simple.

Accepted code:

// 1AC, easy with recursive
/**
 * Definition for binary tree
 * 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;
        if (root == nullptr) {
            return res;
        }
        
        dfs(root, 1, res);
        return res;
    }
private:
    void dfs(TreeNode *ptr, int dep, vector<int> &res) {
        if (dep > res.size()) {
            res.push_back(ptr->val);
        }
        
        if (ptr->right != nullptr) {
            dfs(ptr->right, dep + 1, res);
        }
        if (ptr->left != nullptr) {
            dfs(ptr->left, dep + 1, res);
        }
    }
};