LetsFindOut.cs

using System.Linq;
using Xunit;

namespace MinDeletions
{
    public class LetsFindOut
    {
        public static int GetMinDeletions(string s)
        {
            return s.Length - s.ToCharArray().Distinct().Count();
        }
    }

    public class UnitTest1
    {
        [Fact]
        public void Test1()
        {
            var code = "abcabc";
            var result = LetsFindOut.GetMinDeletions(code);
            Assert.Equal(3, result);
        }

        [Fact]
        public void Test2()
        {
            var code = "bbeadcebfp";
            var result = LetsFindOut.GetMinDeletions(code);
            Assert.Equal(3, result);
        }

        [Fact]
        public void Test3()
        {
            var code = "ffcccdndha";
            var result = LetsFindOut.GetMinDeletions(code);
            Assert.Equal(4, result);
        }

        [Fact]
        public void Test4()
        {
            var code = "afcbdgigdrfacaafgbgeecadajadadebbofbdcaaidacacbdflbcfdbgaaidoaaafacaaiccdafhkcgaeeffebchbbaebfhiciabeaaabbmaefbagaabcafccbbaqdefaggddnjdafdibbeahjcjgebeddbababdgaegcbdcfbgabfhccecdibdccchbhbaccaebcbadbcecefcefcbdildkebngadeekasbbgfcafcfhbcafaaibcbcbickaaedafiaedbbccgpdedaccccclbggcoccaepbdaadgdfdbdbdfacbcacdaaabafadcibcbcbeehbffagibbabbcagbccbdcdddccdcdeahaafamngadgbcaaceeheabfcbedcfbbcbfacdagdaboddagfbaeagcbbclbcibcibhejceabdacbejfcdfbebccaggbcabdgiglcceaagaacchddacicacacgcbdffbogafcaacigdgcafcagbcaccbabecacahcdcgbhbgdcdcedagbaibbdadbkhcahbeaaaacbacagbaagbjcfaeadboakcaiacdaggfdgchacdjjpbalhadbbcfiaacdbeaidbeccebgajbifacblbbbcccebbemfancibbcdcdbbbadmlioqkccchcaiebacdaiddedgdbhifaccfaaaaebdffbbgdcbdefbhaabecdahfdjbfadaaabffdghhlabbabeaqdflkfcbbaaeeaeamocagaadabcdheafihbbgjhameiagdcjaahkadcibaafbacaadodakkdacgbdbffdbjmbbbafgddebihcaaaaeahhbhbbabhhdfdefcfeecadbgagicbebcambebcdeaaakgnbaacaafgfjagbbdeebgebdgbabdadgageachajedabcfekbebccgaacbfbfddbhaafdgmachacgdadaebgbadlbacjddbcbcaccbbjancdd";
            var result = LetsFindOut.GetMinDeletions(code);
            Assert.Equal(981, result);
        }
    }
}