How do I check if my array has repeated values inside it?

take look at my implementation its generic and efficient

public static bool HasDuplicates<T>(IList<T> items)
    {
        Dictionary<T, bool> map = new Dictionary<T, bool>();
        for (int i = 0; i < items.Count; i++)
        {
            if (map.ContainsKey(items[i]))
            {
                return true; // has duplicates
            }
            map.Add(items[i], true);
        }
        return false; // no duplicates
    }

here are some calls

string[] strings = new[] { "1", "2", "3" };
Utility.HasDuplicates(strings)// this will return false

int[] items=new []{1,2,3,1};
Utility.HasDuplicates(items)// this will return true

Use this:

bool CheckUniqueness(double[] values)
{
    var uniqueValues = new HashSet<double>();
    foreach (double d in values)
    {
        if(uniqueValues.Contains(d))
        {
            return false;
        }
        uniqueValues.Add(d);
    }
    return true;
}

You could do this with a little Linq:

if (testArray.Length != testArray.Distinct().Count())
{
    Console.WriteLine("Contains duplicates");
}

The Distinct extension method removes any duplicates, and Count gets the size of the result set. If they differ at all, then there are some duplicates in the list.

Alternatively, here's more complicated query, but it may be a bit more efficient:

if (testArray.GroupBy(x => x).Any(g => g.Count() > 1))
{
    Console.WriteLine("Contains duplicates");
}

The GroupBy method will group any identical elements together, and Any return true if any of the groups has more than one element.

Both of the above solutions work by utilizing a HashSet<T>, but you can use one directly like this:

if (!testArray.All(new HashSet<double>().Add))
{
    Console.WriteLine("Contains duplicates");
}

Or if you prefer a solution that doesn't rely on Linq at all:

var hashSet = new HashSet<double>();
foreach(var x in testArray) 
{
    if (!hashSet.Add(x)) 
    {
        Console.WriteLine("Contains duplicates");
        break;
    }
}