Tukukkk

Suppose I have two arrays as follows

int first = { 1, 2, 3, 4, 5, 6, 12, 13, 14 };

int second = { 12, 13, 14, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9 };

I want the result as follows:

matching index from the first = 6,7,8 

matching index from second = 0,1,2 

Condition: I cannot sort the array to find the index and there can be any number of the array.

I am looking for some efficient solution and I will be glad for the help.
Thanks in advance.

Below is the code I did for the two arrays:

class Program

{

    static void Main(string args)

    {

        int first = { 1, 2, 3, 4, 5, 6, 12, 13, 14 };

        int second = { 12, 13, 14, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9 };

        IndexArray sameIndexArray = CompareArray(first, second);

        Console.WriteLine("FOLLOWING ARE THE INDEX WITH SAME VALUE FOR FIRST ARRAY");

        foreach (var index in sameIndexArray.FirstArray)

        {

            Console.WriteLine(index);

        }

        Console.WriteLine("FOLLOWING ARE THE INDEX WITH SAME VALUE FOR SECOND ARRAY");

        foreach (var index in sameIndexArray.SecondArray)

        {

            Console.WriteLine(index);

        }



        Console.ReadKey();

    }



    private static IndexArray CompareArray(int firstArray, int secondArray)

    {

        IndexArray arrayIndex = new IndexArray();

        arrayIndex.FirstArray = new List<int>();

        arrayIndex.SecondArray = new List<int>();

        for (int i = 0; i < firstArray.Length; i++)

        {

            for (int j = 0; j < secondArray.Length; j++)

            {

                if (firstArray[i] == secondArray[j])

                {

                    arrayIndex.FirstArray.Add(i);

                    arrayIndex.SecondArray.Add(j);

                }

            }

        }



        return arrayIndex;

    }

}



public class IndexArray

{

    public List<int> FirstArray { get; set; }

    public List<int> SecondArray { get; set; }

}

Your solution is O(N^2). An O(N) or O(N log N) solution should be possible:

• Create a HashSet for each of the sets


• iterate over the first set, filtering by hashset2.Contains and print the indexes


• do the same vice versa

Something like this:

private static IndexArray CompareArray(int firstArray, int secondArray)

{

    IndexArray arrayIndex = new IndexArray();

    var hashset2 = new HashSet<int>(secondArray);

    for (int i = 0; i < firstArray.Length; i++)

    {

        if (hashset2.Contains(firstArray[i]))

            arrayIndex.FirstArray.Add(i);

    }

    var hashset1 = new HashSet<int>(firstArray);

    for (int i = 0; i < secondArray.Length; i++)

    {

        if (hashset1.Contains(secondArray[i]))

            arrayIndex.SecondArray.Add(i);

    }



    return arrayIndex;

}

If this is working code it might be a better fit on code review.

I would drop the

arrayIndex.FirstArray = new List<int>();

arrayIndex.SecondArray = new List<int>();

Add

public List<int> FirstArray  { get; } = new List<int>();

public List<int> SecondArray { get; } = new List<int>();

Arraylookup is fast but I would add

int first = firstArray[i];

And then use that.

WritelLine will write a line.