//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].

/**
 * 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) {
        // 199. Binary Tree Right Side View
        vector<int> res;
        if(root==NULL){
            return res;
        }

        queue<TreeNode*> q;
        q.push(root);

        while(! q.empty()){
            TreeNode* node=q.front();
            res.push_back(node->val);
            q.pop();    

            if(node->right){
                q.push(node->right);
            }

            if(node->left){
                q.push(node->left);
            }
        }
        
        return res;
    }
};