Getting all the combinations in an array

Question

Say I have the following array:

var arr = new[] { "A", "B", "C" };

How can I produce all the possible combinations that contain only two characters and no two the same (e.g. AB would be the same as BA). For example, using the above array it would produce:

AB
AC
BC

Please note that this example has been simplified. The array and the length of the string required will be greater.

I'd really appreciate if someone could help.

Answer 1

This code

var strs = new[] {"A", "B", "C", "D"};
var combinations = CreateCombinations(0, "", strs);
var text = string.Join(", ", combinations);

private List<string> CreateCombinations(int startIndex, string pair, string[] initialArray)
    {
        var combinations = new List<string>();
        for (int i = startIndex; i < initialArray.Length; i++)
        {
            var value = $"{pair}{initialArray[i]}";
            combinations.Add(value);
            combinations.AddRange(CreateCombinations(i + 1, value, initialArray));
        }

        return combinations;
    }

The text variable will contain

A, AB, ABC, ABCD, ABD, AC, ACD, AD, B, BC, BCD, BD, C, CD, D