题目链接：力扣

 解题思路：

AC代码

class Solution {
    List<Integer> tem = new ArrayList<>();
    List<List<Integer>> result = new ArrayList<>();
    public  List<List<Integer>> combine(int n, int k) {
        process(n, k, 1);
        return result;
    }
    public  void process(int n, int k, int cur) {
        if (tem.size() + n - cur + 1 < k) {
            return;
        }
        if (tem.size() == k) {
            result.add(new ArrayList<>(tem));
            return;
        }
        tem.add(cur);
        process(n, k, cur + 1);
        tem.remove(tem.size() - 1);
        process(n, k, cur + 1);
    }
}