Equal values in array [duplicate]

Question

How can I check if there are two or more equal values in one array?

eg. in this example, i want the program to tell me that there is a pair of 2 and a pair of 4

int[] array1 = { 1, 2, 4, 2, 4 };

Answer 1

Using Linq

var result = array1.GroupBy(i=>i)
                .Select(g=>new {Value = g.Key, Count = g.Count()})
                .Where(x=>x.Count>1)
                .ToList();

foreach (var pair in result)
{
     Console.WriteLine("PAIR: " + pair.Value + " COUNT: " + pair.Count);
}

Answer 2

[EDIT] Sorry, this answers the question "How can I check if there are two or more equal values in one array?", but it doesn't tell you the actual duplicates...

---

This would work, but possibly it isn't the most efficient way!

int[] array1 = { 1, 2, 4, 2, 4 };

if (array1.Distinct().Count() < array1.Length)
    Console.WriteLine("Contains Dupes");

If you want the most efficient approach:

bool containsDupes(int[] array)
{
    for (int i = 0; i < array.Length - 1; ++i)
    {
        int n = array[i];

        for (int j = i+1; j < array.Length; ++j)
            if (array[j] == n)
                return true;
    }

    return false;
}

I don't think you can get much more efficient than that. It will return as soon as it finds any match.