Список <T> Бинарный поиск возвращает неправильное значение

Обновление № 2: двоичный поиск с использованием пользовательского сопоставления в списке с дубликатами.

Предполагая, что в "1707 ABCD", "1707" есть DateDetails а "ABCD" - это TrackDetails, у вас есть массив данных с двумя полями, которые уже отсортированы по порядку одного из двух полей, а именно DateDetails. Таким образом, может быть несколько записей с теми же DateDetails.

Если вы выполните BinarySearch, он вернет одну из записей с указанными DateDetails, не обязательно первой. Затем вы должны отсканировать назад, чтобы найти первый.

public static class ListHelper
{
    /// <summary>
    /// Return the zero-based index of the first matching item in the sorted List, 
    /// if a match for item is found; otherwise, a negative number that is the bitwise 
    /// complement of the index of the next element that is larger than item or, if there is
    /// no larger element, the bitwise complement of Count.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="list"></param>
    /// <param name="item"></param>
    /// <param name="comparer"></param>
    /// <returns>The zero-based index of the first matching item in the sorted List, 
    /// if item is found; otherwise, a negative number that is the bitwise complement 
    /// of the index of the next element that is larger than item or, if there is
    /// no larger element, the bitwise complement of Count.</returns>
    public static int BinarySearchFirst<T>(this List<T> list, T item, IComparer<T> comparer)
    {
        int start = list.BinarySearch(item, comparer);
        for (; start > 0 && comparer.Compare(list[start], list[start - 1]) == 0; start--)
            ;
        return start;
    }
    /// <summary>
    /// Find the zero-based indices of the first and last matching items in the sorted List, 
    /// if a match for item is found; otherwise, a negative number for both that is the bitwise 
    /// complement of the index of the next element that is larger than item or, if there is
    /// no larger element, the bitwise complement of Count.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="list"></param>
    /// <param name="item"></param>
    /// <param name="comparer"></param>
    /// <param name="start">The zero-based index of the first matching item in the List, 
    /// if item is found; otherwise, a negative number that is the bitwise complement 
    /// of the index of the next element that is larger than item or, if there is
    /// no larger element, the bitwise complement of Count.</param>
    /// <param name="end">The zero-based index of the first matching item in the sorted List, 
    /// if item is found; otherwise, a negative number that is the bitwise complement 
    /// of the index of the next element that is larger than item or, if there is
    /// no larger element, the bitwise complement of Count.</param>
    /// <returns>true if found, else false</returns>
    public static bool BinarySearchRange<T>(this List<T> list, T item, IComparer<T> comparer, out int start, out int end)
    {
        start = end = list.BinarySearch(item, comparer);
        if (start < 0)
            return false;
        for (; start > 0 && comparer.Compare(list[start], list[start - 1]) == 0; start--)
            ;
        for (int last = list.Count - 1; end < last && comparer.Compare(list[end], list[end + 1]) == 0; end++)
            ;
        return true;
    }
}