Level_Order_Traversal.cpp

vector<vector<int>> LevelOrderTraversal(TreeNode *root) {
    vector<vector<int>> ans;
    if(root == NULL) return ans;
    queue<TreeNode*> q;
    q.push(root);
    
    while(!q.empty()) {
        int size = q.size();
        vector<int> level;
        
        for(int i=0; i<size; i++) {
            TreeNode *node = q.front();
            q.pop();
            if(node -> left != NULL) q.push(node -> left);
            if(node -> right != NULL) q.push(node -> right);
            level.push_back(node -> val);
        }
        ans.push_back(level);
    }
    return ans;
}