如何比较 C# 中的两个列表？

Question

I have two lists to compare:

I want to compare List A and List B such that if any of the dates from ListB is present in List A then return true.

For example, if 14-01-2020 (which is in List B) is present in List A (which is definitely present) then it should return true.

How to do that?

Please note: The data in List A contains the dates of an entire month, whereas List B contains only a few dates.

Answer 1

If any of the dates from ListB is present in List A then return true.

 return ListB.Any(x => ListA.Contains(x));

or vice versa:

 return ListA.Any(x => ListB.Contains(x));

Which one is better for you will depend on the nature of your data, but I'd normally favor running Contains() over the shorter sequence.

Additionally, I see this:

The data in List A contains the dates of an entire month

Depending on exactly what you mean, you may be able to take advantange of that fact:

var start = A.Min(x => x);
var stop = A.Max(x => x);
return ListB.Any(x => x >= start && x <= stop);

Finally, if you know the data in one or both of the sequences is sorted, you can optimize these significantly.