Solution: Unique Number of Occurrences

Statement

Given an array of integers nums, return TRUE if each value in the array has a unique number of occurrences; otherwise, return FALSE.

Constraints:

• $1$<= nums.length <=$1000$

• $-1000$ <= nums[i] <= $1000$

Solution

The algorithm checks if there is a unique number of occurrences of each element by using a hash map and a hash set. First, for each element of the nums array, put the element in the hash map if it does not already exist in the hash map; otherwise, increment its count. Second, put all the elements' frequencies (counts) in a hash set. Finally, the algorithm will return TRUE if the count of the hash map and the hash set is the same and FALSE otherwise.

The algorithm to solve this problem ...