No expert on algorithms, but: Sorting an array is O(n*log(n)) Hashmap operations are constant time, and walking through array to put stuff in it is O(n) So,

No expert on algorithms, but: Sorting an array is O(n*log(n)) Hashmap operations are constant time, and walking through array to put stuff in it is O(n) So, implementation based on Hashmap should be slightly faster. It requires extra memory, though.