Hash

#define MOD
vector < pair < int , int > > Hash[MOD];

void Insert (int x) {
  int key = x % MOD;
  for (size_t it = 0; it < Hash[key].size(); ++it)
    if (Hash[key][it].first == x) {
      Hash[key][it].second ++;
      return;
    }
  Hash[key].push_back({x, 1});
}

void Erase (int x) {
  int key = x % MOD;
  vector < pair < int , int > > :: iterator it;
  for (it = Hash[key].begin(); it != Hash[key].end(); ++it)
    if (it -> first == x) {
      it -> second --;
      if (it -> second == 0)
        Hash[key].erase (it);
      return;
    }
}

int Search (int x) {
  int key = x % MOD;
  for (auto it : Hash[key])
    if (it.first == x)
      return it.second;
  return 0;
}