public void Test1()
        {
            var text = "bcabc";

            var result = new RemoveDuplicatesFromString().RemoveDuplicateLetters(text);

            Assert.That(result, Is.EqualTo("abc"));
        }
        public void Test4()
        {
            var text = "leetcode";

            var result = new RemoveDuplicatesFromString().RemoveDuplicateLetters(text);

            Assert.That(result, Is.EqualTo("letcod"));
        }