What is the most efficient data structure for storing a list of integers that you need to search a lot in .Net?

Question

I need an efficient data structure to store a list of integers. The amount in the list can vary from 1 to probably not more than 1000. The list will be requested approximately 20 times per request. What would be the most efficient type of collection to store?

UPDATE

To give a little more information, we'll take www.wikipediamaze.com (the little game I wrote) as an example (not a real scenario, but close enough for a conversation). For the list of puzzles on any given page, I am currently returning a list from the puzzle table connected to the table in which the puzzles that the current user played are stored. Instead, I want to cache a list of puzzles that are independent of the user. So what I'm doing is the first load and cache the list of puzzles from the database. Then I load and cache the list of puzzles that the user played. Then, when I repeat the puzzles to display them, I want to do this:

protected BestDataStructure<long> PlayedPuzzles {get; set;} //Loaded from session

protected bool HasBeenPlayed(long puzzleId)
{
    return PlayedPuzzles.Contains(puzzleId)
}

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Answer 1

, , , HashSet<int>, .

O (1), . HashSet.Contains O (1).

: HashSet, , . Contains() HashSet; . , , , .

Answer 2

, ​​, Contains(), HashSet<int> - , . HashSet<int> - O (1) ( ) Contains(), , .

Answer 3

HashSet (int) .

Answer 4

if you need to check for an element and then probably bool[]with 1000 elements and set true for existing integer elements?