Method set8Perm

app/src/main/java/solver/Utils.java:39–51

(int[] arr, int len, int idx)

    public static int[] fact = {1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600};
    public static void set8Perm(int[] arr, int len, int idx) {
        int val = 0x76543210;
        for (int i = 0; i < len - 1; i++) {
            int p = fact[len - 1 - i];
            int v = idx / p;
            idx -= v * p;
            v <<= 2;
            arr[i] = (val >> v) & 0x7;
            int m = (1 << v) - 1;
            val = (val & m) + ((val >> 4) & ~m);
        }
        arr[len - 1] = val & 0x7;
    }

    public static int get8Perm(int[] arr, int len) {
        int idx = 0;