遞歸函數，以數組形式返回結果

Question

如何更改此函數以將String[][]作為返回類型並返回可能組合的數組，而不僅僅是打印找到的組合？

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);
    }
}

例：

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

應該回來

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

Answer 1

您可以這樣做：

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.
}

但是，最好將allResults作為ArrayList<String[]> 。