问c#字符串比较方法返回第一个不匹配的索引

EN

/// <summary>
/// Gets a first different char occurence index
/// </summary>
/// <param name="a">First string</param>
/// <param name="b">Second string</param>
/// <param name="handleLengthDifference">
/// If true will return index of first occurence even strings are of different length
/// and same-length parts are equals otherwise -1
/// </param>
/// <returns>
/// Returns first difference index or -1 if no difference is found
/// </returns>
public int GetFirstBreakIndex(string a, string b, bool handleLengthDifference)
{
    int equalsReturnCode = -1;
    if (String.IsNullOrEmpty(a) || String.IsNullOrEmpty(b))
    {
        return handleLengthDifference ? 0 : equalsReturnCode;
    }

    string longest = b.Length > a.Length ? b : a;
    string shorten = b.Length > a.Length ? a : b;    
    for (int i = 0; i < shorten.Length; i++)
    {
        if (shorten[i] != longest[i])
        {
            return i;
        }
    }

    // Handles cases when length is different (a="1234", b="123")
    // index=3 would be returned for this case
    // If you do not need such behaviour - just remove this
    if (handleLengthDifference && a.Length != b.Length)
    {
        return shorten.Length;
    }

    return equalsReturnCode;
}

public static int Your_Name_Here(this string s, string other) 
{
    string first = s.Length < other.Length ? s : other;
    string second = s.Length > other.Length ? s : other;

    for (int counter = 0; counter < first.Length; counter++)
    {
        if (first[counter] != second[counter])
        {
            return counter;
        }
    }
    return -1;
}

public static int FirstUnmatchedIndex(this string x, string y)
{
  if(x == null || y == null)
    throw new ArgumentNullException();
  int count = x.Length;
  if(count > y.Length)
    return FirstUnmatchedIndex(y, x);
  if(ReferenceEquals(x, y))
    return -1;
  for(idx = 0; idx != count; ++idx)
    if(x[idx] != y[idx])
      return idx;
  return count == y.Length? -1 : count;
}