102 Binary Tree Level Order Traversal

我也不知道這要記錄什麼, 就是bfs記錄每層的節點吧

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