WEI-CHENG CHEN

解法

class Solution {
public:
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        if(!root) return {};
        vector<vector<int>> ans;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()){
            int n = q.size();
            vector<int> temp;
            for(int i=0;i<n;i++){
                // 節點取出
                TreeNode* node = q.front();
                q.pop();
                // 裝進去
                temp.push_back(node->val);
                // BFS
                if (node->left) q.push(node->left);
                if (node->right) q.push(node->right);
            }
            ans.push_back(temp);
        }
        reverse(ans.begin(), ans.end()); // 最後答案反轉
        return ans;
    }
};