public static int DuplicateBinarySearch <T, TTarget>(
[NotNull] this IList <T> values,
[NotNull] SingleComparer <TTarget> comparer,
[NotNull] Func <T, TTarget> converter)
{
if (comparer == null)
{
throw new ArgumentNullException(nameof(comparer));
}
if (values.Count == 0)
{
return(-1);
}
int start = 0;
int end = values.Count - 1;
int midIndex = end / 2;
int firstOccuranceIndex = -1;
TTarget midItem = converter.Invoke(values[midIndex]);
int compareResult = comparer.Compare(midItem);
while (start <= end)
{
if (compareResult < 0)
{
start = midIndex + 1;
}
else
{
end = midIndex - 1;
if (compareResult == 0)
{
firstOccuranceIndex = midIndex;
}
}
midIndex = (start + end) / 2;
midItem = converter.Invoke(values[midIndex]);
compareResult = comparer.Compare(midItem);
}
return(firstOccuranceIndex);
}
