binary-tree-level-order-traversa

class Solution {
public:
    vector<vector<int> > levelOrder(TreeNode *root) {
        queue<TreeNode*>q;
        vector<vector<int>>ans;
        if(!root)return ans;
        q.push(root);
        while(!q.empty())
        {
            int size=q.size();
            vector<int>temp;
            while(size--)
            {
                TreeNode*top=q.front();
                q.pop();
                temp.push_back(top->val);
                if(top->left)q.push(top->left);
                if(top->right)q.push(top->right);
            }
            ans.push_back(temp);
        }
        return ans;
    }
};