102.binary-tree-level-order-traversal.cpp

class Solution
{
public:
    vector<vector<int>> levelOrder(TreeNode *root)
    {
        vector<vector<int>> ans;
        if(!root) return ans;
        queue<TreeNode *> q;
        q.push(root);
        while (!q.empty())
        {
            vector<int> vtr;
            int size=q.size();
            for (int i = 0; i < size; i++)
            {
                TreeNode* curr=q.front();
                q.pop();
                if(curr->left){
                    q.push(curr->left);
                }
                if(curr->right){
                    q.push(curr->right);
                }
                vtr.push_back(curr->val);
            }
            ans.push_back(vtr);
        }
        return ans;
    }
};