topic description
output an array of elements whose occurrence times are greater than n
add a findDuplicate (n) method for all array objects to return a list of elements whose occurrence frequency > = n in the array
[1, findDuplicate (2) = > [1]
[1, findDuplicate (5) = > []
[1, 2, 3, 4, 4, 1, 2, 2, 2] = > findDuplicate (- 1) = > [1, 2, 3, 4, 4]