How do I check for duplicate answers in this array? c#

Question

Sorry for the newbie question. Could someone help me out? Simple array here. What's the best/easiest method to check all the user input is unique and not duplicated? Thanks

    private void btnNext_Click(object sender, EventArgs e)
    {

        string[] Numbers = new string[5];


        Numbers[0] = txtNumber1.Text;
        Numbers[1] = txtNumber2.Text;
        Numbers[2] = txtNumber3.Text;
        Numbers[3] = txtNumber4.Text;
        Numbers[4] = txtNumber5.Text;


        foreach (string Result in Numbers)
        {
            lbNumbers.Items.Add(Result);
        }

        txtNumber1.Clear();
        txtNumber2.Clear();
        txtNumber3.Clear();
        txtNumber4.Clear();
        txtNumber5.Clear();
    }
}

}

I should have added I need to check to happen before the numbers are output. Thanks

Answer 1

One simple approach is via LINQ:

bool allUnique = Numbers.Distinct().Count() == Numbers.Length;

Answer 2

Another approach is using a HashSet<string>:

var set = new HashSet<string>(Numbers);
if (set.Count == Numbers.Count)
{ 
    // all unique
}

or with Enumerable.All:

var set = new HashSet<string>();
// HashSet.Add returns a bool if the item was added because it was unique
bool allUnique = Numbers.All(text=> set.Add(text)); 

Enunmerable.All is more efficient when the sequence is very large since it does not create the set completely but one after each other and will return false as soon as it detects a duplicate.

Here's a demo of this effect: http://ideone.com/G48CYv

• HashSet constructor memory consumption: 50 MB, duration: 00:00:00.2962615
• Enumerable.All memory consumption: 0 MB, duration: 00:00:00.0004254

msdn

The HashSet<T> class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no particular order.