Binary Tree Right Side View

/**
* 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 *> q1,q2;
q1.push(root);
while(!q1.empty()||!q2.empty())
{
if(!q1.empty())
{
TreeNode * temp_num=q1.front();
res.push_back(temp_num->val);
while(!q1.empty())
{
TreeNode * temp=q1.front();
q1.pop();
if(temp->right!=NULL)
q2.push(temp->right);
if(temp->left!=NULL)
q2.push(temp->left);
}
}
else
{
TreeNode * temp_num=q2.front();
res.push_back(temp_num->val);
while(!q2.empty())
{
TreeNode * temp=q2.front();
q2.pop();
if(temp->right!=NULL)
q1.push(temp->right);
if(temp->left!=NULL)
q1.push(temp->left);
}
}
}
return res;
}
};