internal class Hamming {
  public static int Compute(string strand1, string strand2) {
    int ret = 0;
    if(strand1.Length != strand2.Length) {
      throw new System.ArgumentException("Strands must be same length");
    }
    for(int i = 0; i < strand1.Length; i++) {
      if(strand1[i] != strand2[i]) {
        ret++;
      }
    }
    return ret;
  }
}