Easier way to do many nested for loops

Question

I need to generate a list of all possible combinations of colors(I have 8 different colors) and would like to specify the length of the output, without going into the code and adding another loop.

for (int s1 = 0; s1 < kinds.length; s1++) {
        for (int s2 = 0; s2 < kinds.length; s2++) {
            for (int s3 = 0; s3 < kinds.length; s3++) {
                for (int s4 = 0; s4 < kinds.length; s4++) {
                    for (int s5 = 0; s5 < kinds.length; s5++) {
                        String[] guess = new String[length];
                        guess[0] = colors[s1];
                        guess[1] = colors[s2];
                        guess[2] = colors[s3];
                        guess[3] = colors[s4];
                        guess[4] = colors[s5];
                        Possible.add(guess);

                    }
                }
            }
        }
    }

Possible duplicate of [Getting every possible permutation of a string or combination including repeated characters in Java](http://stackoverflow.com/questions/5113707/getting-every-possible-permutation-of-a-string-or-combination-including-repeated) — ACascarino, Dec 31 '16 at 02:41
Possible duplicate of [Combinatorics: generate all “states” - array combinations](http://stackoverflow.com/q/9632677/5221149) — Andreas, Dec 31 '16 at 03:38
Possible duplicate of [how to write n-level embeded loop with java](http://stackoverflow.com/q/40954694/5221149) — Andreas, Dec 31 '16 at 03:45

pt2121 · Answer 1 · 2017-01-01T15:46:43.250

You can use recursion instead of loop. The general idea is all possible combinations can be generated from the all possible first colors concat with the combinations of the rest.

private static List<String> possibles = new ArrayList<>();

private static void combi(char[] arr, char[] out, int start, int end, int index, int length) {
    if (index == length) {
        possibles.add(new String(out));
        return;
    }

    for (int i = start; i <= end && end - i + 1 >= length - index; i++) {
        out[index] = arr[i];
        combi(arr, out, i + 1, end, index + 1, length);
    }
}

private static void compute(char[] colors, int length) {
    char[] output = new char[length];
    combi(colors, output, 0, colors.length - 1, 0, length);
}

public static void main(String[] args) {
    char[] colors = {'a', 'b', 'c', 'd', 'e'};
    int length = 3;
    compute(colors, length);

    for (String possible : possibles) {
        System.out.println(possible);
    }
}

@KaminPallaghy updated my answer. Let me know if it's still not clear. — pt2121, Jan 01 '17 at 15:51

Easier way to do many nested for loops

1 Answers1