CODEWITHSUNDEEP
c#arrayslistcontainsexists
SR_
SR_

Reputation: 147

Search for an existing object in a list

This is my first question here so I hope I'm doing right.
I have to create a List of array of integer:

List<int[]> finalList = new List<int[]>();

in order to store all the combinations of K elements with N numbers.

For example:

N=5, K=2 => {1,2},{1,3},{1,4},...

Everything is all right but I want to avoid the repetitions of the same combination in the list({1,2} and {2,1} for example). So before adding the tmpArray (where I temporally store the new combination) in the list, I want to check if it's already stored.

Here it's what I'm doing:

but it doesn't work. Can anyone help me with this issue?

Upvotes: 1

Views: 124

Answers (2)

Shar1er80
Shar1er80

Reputation: 9041

If I remember correctly, contains will either check the value for value data types or it will check the address for object types. An array is an object type, so the contains is only checking if the address in memory is stored in your list. You'll have to check each item in this list and perform some type of algorithm to check that the values of the array are in the list.

Linq, Lambda, or brute force checking comes to mind.

BrokenGlass gives a good suggestion with Linq and Lambda.

Brute Force:

bool itemExists = true;
foreach (int[] ints in finalList)
{
    if (ints.Length != tmpArray.Length)
    {
        itemExists = false;
        break;
    }
    else
    {
        // Compare each element
        for (int i = 0; i < tmpArray.Length; i++)
        {
            if (ints[i] != tmpArray[i])
            {
                itemExists = false;
                break;
            }
        }

        // Have to check to break from the foreach loop
        if (itemExists == false)
        {
            break;
        }
    }
}

if (itemExists == false)
{
    finalList.add(tmpArray);
}

Upvotes: 0

BrokenGlass
BrokenGlass

Reputation: 160852

Array is a reference type - your Contains query will not do what you want (compare all members in order).

You may use something like this:

if (!finalList.Any(x => x.SequenceEqual(tmpArray))
{
    finalList.Add(tmpArray);
}

(Make sure you add a using System.Linq to the top of your file)

I suggest you learn more about value vs. reference types, Linq and C# data structure fundamentals. While above query should work it will be slow - O(n*m) where n = number of arrays in finalList and m length of each array.

For larger arrays some precomputing (e.g. a hashcode for each of the arrays) that allows you a faster comparison might be beneficial.

Upvotes: 2

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