int val;

TreeNode* left;

TreeNode* right;

TreeNode(int _val) { val = _val; }

deque<TreeNode*>* dq = new deque<TreeNode*>();

if (root != nullptr) {

dq->emplace_back(root);

}

vector<vector<int>>* res = new vector<vector<int>>();

for (int level = 0; !dq->empty(); level++) {

vector<int>* curr = new vector<int>();

for (int size = (int)dq->size(); size > 0; size--) {

TreeNode* node = dq->front();

dq->pop_front();

curr->push_back(node->val);

if (node->left != nullptr) {

dq->emplace_back(node->left);

}

if (node->right != nullptr) {

dq->emplace_back(node->right);

}

}

res->emplace_back(*curr);

}

return *res;