199 Binary Tree Right Side View

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].

Solution

/**
 * 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;
        if ( root == NULL ) return res;
        vector<TreeNode*> tmp(1, root);
        while ( tmp.size() != 0 ) {
            int ntmp = tmp.size();
            res.push_back(tmp[ntmp-1]->val);
            vector<TreeNode*> tmp2;
            for ( int i = 0; i <= ntmp-1; i++ ) {
                if ( tmp[i]->left != NULL ) tmp2.push_back(tmp[i]->left);
                if ( tmp[i]->right != NULL ) tmp2.push_back(tmp[i]->right);
            }
            tmp = tmp2;
        }
        return res;
    }
};