public void MissingNumber_1()
        {
            var solution = new _1228_MissingNumberInArithmeticProgression();
            var result   = solution.MissingNumber(new int[] { 5, 7, 11, 13 });

            Assert.AreEqual(9, result);
        }
        public void MissingNumber_4()
        {
            var solution = new _1228_MissingNumberInArithmeticProgression();
            var result   = solution.MissingNumber(new int[] { 4, 4, 4, 4 });

            Assert.AreEqual(4, result);
        }