1. A string similarity apparatus comprising: a memory configured to store a plurality of software instructions; and a processor configured to execute the plurality of software instructions, which comprise: determining a first number of characters contained by a first string; determining a second number of characters contained by a second string; determining a larger number from among the first number and the second number; setting the larger number to a string length value; determining a maximum number of subsequent characters from the first strings which match subsequent characters from the second string and setting the value; setting the maximum number to a maximum group size value; calculating a resulting value by subtracting the maximum group size value from the string length value; and outputting the resulting value which represents a computational cost of converting the first string into the second string.