RotationalHash.java

public class RotationalHash {

    public static int hash(String beads) {
        byte[] buf = beads.getBytes();
        int hash = hashBytes(buf);
        int i = 0;
        int j = buf.length - 1;
        while (i < j) {
            buf[i] ^= buf[j];
            buf[j] ^= buf[i];
            buf[i] ^= buf[j];
            i++;
            j--;
        }
        return hash * hashBytes(buf);
    }

    public static int hashBytes(byte[] buf) {
        int windowHash = IntStream.range(0, buf.length)
                .map(i -> buf[i] << i)
                .sum();
        int hash = 1;

        for (int start = 0; start < buf.length; start++) {
            windowHash = (windowHash - buf[start]) >> 1;
            windowHash += buf[start] << (buf.length - 1);
            hash *= windowHash;
        }
        return hash;
    }
}