Jewels and Stones Problem & Solution

#pragma GCC optimize("Ofast,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:
  int numJewelsInStones(string jewels, string stones) {
    unordered_set<char> s{jewels.begin(), jewels.end()};

    int result = 0;
    for (char c : stones) {
      if (s.find(c) != s.end()) {
        ++result;
      }
    }

    return result;
  }
};