Method permToIdx

app/src/main/java/solver/Utils.java:115–124

(int[] permutation, int length, boolean even)

    // permutation
    public static int permToIdx(int[] permutation, int length, boolean even) {
        int index = 0;
        int end = even ? length - 2 : length - 1;
        for (int i = 0; i < end; i++) {
            index *= length - i;
            for (int j = i + 1; j < length; j++)
                if (permutation[i] > permutation[j]) index++;
        }
        return index;
    }

    public static void idxToPerm(int[] permutation, int index, int length, boolean even) {
        int sum = 0;