Write a function named countDuplicates that accepts an array as a parameter and that returns the number of duplicate values in the array.
A duplicate value is a value that also occurs earlier in the array.
For example, if an array named a contains [1, 4, 2.5, 4, "7", 1, 1, 9, 2, "7", 7, false, 3, 4, 1], then the call of countDuplicates(a) should return 6 because there are three duplicates of the value 1, one duplicate of the string value "7", and two duplicates of the value 4.
You may assume that the array passed is non-null and that non of the elements in the array are null or undefined.
Constraints:
The array could be empty or could contain only a single element; in such cases, your function should return 0.
Do not modify the contents of the array.
