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].

answer:

vector<int> rightSideView(TreeNode* root) {        vector<int> result;        TreeNode* t = root;        queue<TreeNode*> current;        queue<TreeNode*> next;        if(root == NULL)return result;        result.push_back(root->val);        if(root->left)current.push(root->left);        if(root->right)current.push(root->right);        while(!current.empty()){            while(!current.empty()){                if(current.size() == 1)result.push_back(current.front()->val);                t = current.front();                current.pop();                if(t->left)next.push(t->left);                if(t->right)next.push(t->right);            }            while(!next.empty()){                current.push(next.front());                next.pop();            }        }        return result;    }