java如何把 一个数组元素的所有排列组合合成一个类

Question

请教如何把static void combinationUtil() 取消, 然后合成到 public static void main (String[] args), 或者该如何 在public static void main (String[] args) 里面做一个双数组 data2[][], 然后把 combinationUtil()里面的 data[] 存到 data2[][]

class permutation {

static void combinationUtil(int arr[], int data[], int start, int end, int index, int r)
{
    if (index == r)
    {
        for (int j=0; j<r; j++)
            System.out.print(data[j]+" ");
        System.out.println("");
        return;
    }

    for (int i=start; i<=end && end-i+1 >= r-index; i++)
    {
        data[index] = arr[i];
        combinationUtil(arr, data, i+1, end, index+1, r);
    }
}

public static void main (String[] args) {
    int arr[] = {1, 2, 3, 4, 5,6,7};
    int r = 5;
    int n = arr.length;
    int data[]=new int[r];
    int start=0,end=n-1,index=0;
    combinationUtil(arr, data, start, end, index, r);
}

}

程序运行的结果是
1 2 3 4 5
1 2 3 4 6
1 2 3 4 7
1 2 3 5 6
1 2 3 5 7
1 2 3 6 7
1 2 4 5 6
1 2 4 5 7
1 2 4 6 7
1 2 5 6 7
1 3 4 5 6
1 3 4 5 7
1 3 4 6 7
1 3 5 6 7
1 4 5 6 7
2 3 4 5 6
2 3 4 5 7
2 3 4 6 7
2 3 5 6 7
2 4 5 6 7
3 4 5 6 7

Answer 1

    static void combinationUtil(int arr[], int data[], int start, int end, int index, int r, List<int[]> list)
    {
        if (index == r)
        {
            int[] obj = new int[r];
            for (int j=0; j<r; j++) {
                obj[j] = data[j];
                System.out.print(data[j]+" ");
            }
            list.add(obj);


            System.out.println("");
            return;
        }

        for (int i=start; i<=end && end-i+1 >= r-index; i++)
        {
            data[index] = arr[i];
            combinationUtil(arr, data, i+1, end, index+1, r, list);
        }
    }

    public static void main (String[] args) {
        int arr[] = {1, 2, 3, 4, 5,6,7};
        int r = 5;
        int n = arr.length;
        int data[]=new int[r];
        int start=0,end=n-1,index=0;
        List<int[]> list = new ArrayList<>();
        combinationUtil(arr, data, start, end, index, r, list);

    }