/// <summary>
/// Reports the zero-based index of the first occurrence of the specified collection in this instance
/// and uses the specified <see cref="IEqualityComparer{T}"/>.
/// The search starts at a specified position.
/// </summary>
/// <param name="s">The current collection.</param>
/// <param name="t">The collection to seek.</param>
/// <param name="startIndex">The search starting position.</param>
/// <param name="comparer">The specified <see cref="IEqualityComparer{T}"/> instance.</param>
/// <typeparam name="T">The type of element in the collection.</typeparam>
/// <returns>
/// The zero-based index position of value if <paramref name="t"/> is found, or -1 if it is not.
/// If <paramref name="t"/> is empty, the return value is 0.
/// </returns>
/// <exception cref="ArgumentNullException"><paramref name="s"/> or <paramref name="t"/> is null.</exception>
/// <exception cref="ArgumentOutOfRangeException">
/// <paramref name="startIndex"/> is less than zero or greater than <see cref="IReadOnlyCollection{T}.Count">Count</see> of <paramref name="s"/>.
/// </exception>
public static int IndexOf <T>(this IReadOnlyList <T> s, IReadOnlyList <T> t, int startIndex, IEqualityComparer <T> comparer)
where T : IEquatable <T>
{
Validate(s, t, startIndex);
// Follow the behavior of string.IndexOf(string) method.
if (t.Count == 0)
{
return(0);
}
if (s.Count == 0 || s.Count < t.Count)
{
return(-1);
}
if (comparer == null)
{
comparer = EqualityComparer <T> .Default;
}
if (t.Count == 1)
{
return(s.IndexOf(t[0], startIndex, comparer));
}
var table = TableBuilder.BuildTable(t, comparer);
var i = 0;
while (startIndex + i < s.Count)
{
if (comparer.Equals(t[i], s[startIndex + i]))
{
if (i == t.Count - 1)
{
return(startIndex);
}
i++;
}
else
{
if (table[i] > -1)
{
startIndex += i;
i = table[i];
}
else
{
startIndex++;
i = 0;
}
}
}
return(-1);
}
internal static IEnumerable <int> EnumerateIndexes <T>(IReadOnlyList <T> s, IReadOnlyList <T> t, int startIndex, IEqualityComparer <T> comparer)
where T : IEquatable <T>
{
var table = TableBuilder.BuildTable(t, comparer);
var i = 0;
while (startIndex + i < s.Count)
{
if (comparer.Equals(t[i], s[startIndex + i]))
{
if (i == t.Count - 1)
{
yield return(startIndex);
startIndex++;
i = 0;
}
else
{
i++;
}
}
else
{
if (table[i] > -1)
{
startIndex += i;
i = table[i];
}
else
{
startIndex++;
i = 0;
}
}
}
}
