Unique Number of Occurrences Problem & Solution

#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")
#pragma GCC target("avx,avx2,fma")

static const int _=[](){ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();

class Solution {
public:
  bool uniqueOccurrences(vector<int>& arr) {
    unordered_map<int, int> freq;
    for (auto v : arr) {
      ++freq[v];
    }

    unordered_set<int> unique;
    for (auto [k, v] : freq) {
      unique.insert(v);
    }

    return freq.size() == unique.size();
  }
};