void SmallDataTest(int[] a, int expected)
        {
            var solution = new PermMissingElemSolution();

            var result = solution.Solution(a);

            Assert.Equal(expected, result);
        }
        void EmptyDataTest()
        {
            var a = new int[] {};

            var solution = new PermMissingElemSolution();
            var expected = 1;

            var result = solution.Solution(a);

            Assert.Equal(expected, result);
        }