public string Compute(IList <string> numbers)
{
if (numbers.Count > 2)
{
throw new Exception("Incorrect count of numbers to subtract, expecting 2, found: " + numbers.Count.ToString());
}
StringMatrixTransformer smt = new StringMatrixTransformer();
NumercStringUtils nsu = new NumercStringUtils();
bool negateAnswer = ReorderLargerFirst(ref numbers);
IList <IList <int> > matrix = smt.TransformStringListToReversedIntMatrix(numbers);
StringBuilder sb = new StringBuilder();
int i = 0;
for (; i < matrix[1].Count; i++)
{
if (matrix[0][i] < matrix[1][i])
{
SetupCarryAt(matrix[0], i);
}
sb.Append(matrix[0][i] - matrix[1][i]);
}
// get the rest if there's any left in the larger number
for (; i < matrix[0].Count; i++)
{
sb.Append(matrix[0][i]);
}
return(nsu.TrimLeadingZeros(
negateAnswer ?
"-" + smt.ReverseString(sb.ToString()) :
smt.ReverseString(sb.ToString())));
}
