public void CountElementsTest()
{
var s = new Solution();
int[] arr;
arr = new int[] { 1, 2, 3 }; // 2
Assert.Equal(2, s.CountElements(arr));
arr = new int[] { 1, 1, 3, 3, 5, 5, 7, 7 }; // 0
Assert.Equal(0, s.CountElements(arr));
arr = new int[] { 1, 3, 2, 3, 5, 0 }; // 3
Assert.Equal(3, s.CountElements(arr));
arr = new int[] { 1, 1, 1, 1, 2, 2 }; // 4
Assert.Equal(4, s.CountElements(arr));
}