class Solution {
public:
    TreeNode* ans;
    bool dfs(TreeNode* root, TreeNode* p, TreeNode* q) {
        if (root == nullptr) return false;
        bool lson = dfs(root->left, p, q);
        bool rson = dfs(root->right, p, q);
        if ((lson && rson) || ((root->val == p->val || root->val == q->val) && (lson || rson))) {
            ans = root;
        } 
        return lson || rson || (root->val == p->val || root->val == q->val);
    }
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        dfs(root, p, q);
        return ans;
    }
};

class Solution:
    def combine(self, n: int, k: int) -> List[List[int]]:
        if n < k or n < 1:
            return []
        if k == 0:
            return [[]]
        if n == k:
            return [[i for i in range(1, n+1)]]
        ans1 = self.combine(n-1, k-1)
        ans2 = self.combine(n-1, k)
        print(n, k, ans1, ans2)
        if ans1:
            for i in ans1:
                i.append(n)
        return ans1+ans2