Exists 比Contains 慢非常多。

void Main()
{
	List<string> s = new List<string>(){};
	for(int i=0;i<10000;i++)
	{
		s.Add(i.ToString());
	}

	s.Sort();
	

	Stopwatch sw0 = new Stopwatch();
	sw0.Start();
	for(int i=0;i<10000;i++)
	{
		var k0 =  s.Contains(i.ToString());
	}
	sw0.Stop();
	sw0.Elapsed.Dump();
	
	Stopwatch sw1 = new Stopwatch();
	sw1.Start();
	for(int i=0;i<10000;i++)
	{
		var k1 = s.Exists(it=>it==i.ToString());
	}
	sw1.Stop();
	sw1.Elapsed.Dump();
	
		Stopwatch sw2 = new Stopwatch();
	sw2.Start();
	for(int i=0;i<10000;i++)
	{
		var k2 = BinarySearch(s,i.ToString());
	}
	sw2.Stop();
	sw2.Elapsed.Dump();

}

public static bool BinarySearch(List<string> list, string value)
		
		{
			int min = 0;
			int max = list.Count;
			while (min < max)
			{
				int mid = (max + min) / 2;
				string midItem = list[mid];
			
				int comp = midItem.CompareTo(value);
				if (comp < 0)
				{
					min = mid + 1;
				}
				else if (comp > 0)
				{
					max = mid - 1;
				}
				else
				{
					return true;//midItem;
				}
			} 
			if (min == max && min!=list.Count&&
				list[min].CompareTo(value) == 0)
			{
				return true;
			}
		
			return false;
		}

 三个的执行时间。 拆半查找要求得要求先排序。

00:00:00.7093621

00:00:06.7513154

00:00:00.0159961