LeetCode77. 组合

class Solution {
    public static List<List<Integer>> ans = new ArrayList<List<Integer>>();
    public static int[] path = new int[100];
    public static int K;
    public static void dfs(int idx,int n,int k) {//idx [0,n)
        if(k == 0) {
            List<Integer> tmp = new ArrayList<Integer>();
            for(int i = 0;i < K;i++) {
                tmp.add(path[i]);
            }
            ans.add(tmp);
            return;
        }
        for(int i = idx + 1;i <= n;i++) {
            path[k - 1] = i;
            dfs(i, n, k - 1);
        }
    }
    public List<List<Integer>> combine(int n, int k) {
        ans.clear();
        K = k;
        dfs(0,n,k);
        return ans;
    }
}