java - 递归函数，以数组形式返回结果

Question

如何更改此函数以将 String[][] 作为返回类型并返回可能组合的数组，而不是仅打印出找到的组合？

static void combinations2(String[] arr, int len, int startPosition, String[] result){
    if (len == 0){
        System.out.println(Arrays.toString(result));
        return;
    }
    for (int i = startPosition; i <= arr.length-len; i++){
        result[result.length - len] = arr[i];
        combinations2(arr, len-1, i+1, result);
    }
}

示例:

combinations2({ "Value1", "Value2", "Value3" }, 2, 0);

应该返回

{ { "Value1", "Value2" }, {"Value1", "Value3"}, {"Value2", "Value3"} }

Answer 1

你可以这样做:

static void combinations2(String[] arr, int len, int startPosition, String[] result, String[][] allResults){
    if (len == 0){
        //Add result to allResults here
        return;
    }
    for (int i = startPosition; i <= arr.length-len; i++){
        result[result.length - len] = arr[i];
        combinations2(arr, len-1, i+1, result);
    }
}

foo() {
    String[][] allResults = new String[][];
    combinations2(...);
    //allResults now holds all the String[]. 
    //No return statement necessary since arrays, like all Java objects, are passed as references.
}

但你可能会更好地使用 allResults作为ArrayList<String[]> .