c# - 最接近值的元组的二进制搜索列表 >=

Question

给定一个:

List<Tuple<DateTime, int>>

其中提供的列表按 DateTime 值 descending 排序。

如何使用 .BinarySearch() 方法找到 DateTime 为 >= 的值的最小索引指定值？

EG，具有以下值:

[0] = 29th Jan
[1] = 25th Jan
[2] = 20th Jan
[3] = 10th Jan
[4] = 3rd Jan

搜索结果将是:

1st Jan = return 4
5th Jan = return 3
28th Jan = return 0
1st Feb = return something else indicating nothing found (eg -1 or null)

Answer 1

由于您的列表的排序与 BinarySearch 所期望的相反，因此您的比较方法需要返回日期比较结果的倒数:

class TupleCompare : IComparer<Tuple<DateTime,int>> {
    public static readonly TupleCompare Instance = new TupleCompare();
    public int Compare(Tuple<DateTime,int> x, Tuple<DateTime,int> y) {
        return -x.Item1.CompareTo(y.Item1); // Note the negative here
    }
}

有了这个比较器，调用 BinarySearch，检查它的值是否为负，反转它的位，然后减去 1:

DateTime myDate = ... // desired date
int index = list.BinarySearch(Tuple.Create(myDate, 0), TupleCompare.Instance);
if (index < 0) {
    var res = ~index-1;
} else {
    Console.WriteLine("Exact match at index {0}", index);
}

Demo.