leetcode.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) {       vector<int> res;        if(root == NULL)            return res;        queue<TreeNode*> nQueue;        TreeNode *node = root;        nQueue.push(node);        while(!nQueue.empty()){            int size = nQueue.size();            for(int i = 0; i < size; i++){                node = nQueue.front();                nQueue.pop();                if(i == 0)                    res.push_back(node->val);                if(node->right)                    nQueue.push(node->right);                if(node->left)                    nQueue.push(node->left);            }        }        return res;    }};