leetcode-com-explore-challenge-card-july-leetcoding-challenge-544-week-1-july-1st-july-7th-3378.cpp

void levelOrder(vector<vector<int>> &ans, TreeNode *node, int level) {
    if (!node) return;
    if (level >= ans.size())
        ans.push_back({});
    ans[level].push_back(node->val);
    levelOrder(ans,node->left,level+1);
    levelOrder(ans,node->right,level+1);
}
class Solution {
public:
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        vector<vector<int>> ans;
    levelOrder(ans,root,0);
    reverse(ans.begin(),ans.end());
    return ans;
    }
};