public void firstNotRepeatingCharacterTest()
        {
            var f = new FirstNotRepeatingCharacter();

            Assert.AreEqual('c', f.firstNotRepeatingCharacter("abacabad"));
            Assert.AreEqual('_', f.firstNotRepeatingCharacter("abacabaabacaba"));
            Assert.AreEqual('z', f.firstNotRepeatingCharacter("z"));
            Assert.AreEqual('c', f.firstNotRepeatingCharacter("bcb"));
            Assert.AreEqual('_', f.firstNotRepeatingCharacter("bcccccccb"));
            Assert.AreEqual('d', f.firstNotRepeatingCharacter("abcdefghijklmnopqrstuvwxyziflskecznslkjfabe"));
            Assert.AreEqual('_', f.firstNotRepeatingCharacter("zzz"));
            Assert.AreEqual('y', f.firstNotRepeatingCharacter("bcccccccccccccyb"));
            Assert.AreEqual('d', f.firstNotRepeatingCharacter("xdnxxlvupzuwgigeqjggosgljuhliybkjpibyatofcjbfxwtalc"));
            Assert.AreEqual('g', f.firstNotRepeatingCharacter("ngrhhqbhnsipkcoqjyviikvxbxyphsnjpdxkhtadltsuxbfbrkof"));
        }
        public void Test3()
        {
            var result = FirstNotRepeatingCharacter.firstNotRepeatingCharacter("z");

            Assert.AreEqual('z', result);
        }
        public void Test4()
        {
            var result = FirstNotRepeatingCharacter.firstNotRepeatingCharacter("bcb");

            Assert.AreEqual('c', result);
        }
        public void Test2()
        {
            var result = FirstNotRepeatingCharacter.firstNotRepeatingCharacter("abacabaabacaba");

            Assert.AreEqual('_', result);
        }