HashTables

#include <iostream>
#include <string>
#include <unordered_set>
#include <vector>

int Hash(const std::string& key, size_t m) {
  if (key.empty()) return 0;
  return key[0] % m;
}

struct HTNode {
  std::string Key;
  HTNode* Next = nullptr;

  explicit HTNode(const std::string& key) : Key(key) {}
};

// Хеш-таблица строк, разрешающая коллизии методом цепочек.
// Has, Add, Remove.
class HashTable {
 public:
  explicit HashTable(int table_size) : table(table_size, nullptr) {}

  bool Has(const std::string& key) const {
    int hash = Hash(key, table.size());
    HTNode* node = table[hash];
    while (node != nullptr) {
      if (node->Key == key) return true;
      node = node->Next;
    }
    return false;
  }
  bool Add(const std::string& key);
  bool Remove(const std::string& key);

 private:
  std::vector<HTNode*> table;
};

bool HashTable::Add(const std::string& key) {
  // Нужно проверить наличие элемента.
  int hash = Hash(key, table.size());
  HTNode* node = table[hash];
  while (node != nullptr) {
    if (node->Key == key) return false;
    node = node->Next;
  }
  HTNode* new_node = new HTNode(key);
  new_node->Next = table[hash];
  table[hash] = new_node;
  return true;
}

// 1 ->  -> **
bool HashTable::Remove(const std::string& key) {
  int hash = Hash(key, table.size());
  HTNode* node = table[hash];
  HTNode* prev = nullptr;
  while (node != nullptr) {
    if (node->Key == key) {
      (prev ? prev->Next : table[hash]) = node->Next;
      delete node;
      return true;
    }
    prev = node;
    node = node->Next;
  }
  return false;
}

int main1() {
  HashTable table(80);
  char command = 0;
  std::string value;
  while (std::cin >> command >> value) {
    if (command == '+') {
      std::cout << (table.Add(value) ? "OK" : "FAIL") << std::endl;
    } else if (command == '?') {
      std::cout << (table.Has(value) ? "OK" : "FAIL") << std::endl;
    } else if (command == '-') {
      std::cout << (table.Remove(value) ? "OK" : "FAIL") << std::endl;
    }
  }
  return 0;
}

int main() {
/*  int* pointer = new int;
  *pointer = 5;
  std::string s;
  s.length();
  std::string* ps = new std::string("HelloWorld");
  std::cout << *ps;
  std::cout << (*ps).length();
  std::cout << ps->length();*/

  std::unordered_set<std::string> table;
  auto it = table.find("Hello");
  it.operator*();
/*  for (auto i = table.begin(); i != table.end(); ++i) {
    std::cout << *it;
  }
  for (const auto& x : table) {
    std::cout << x;
  }*/
  // Новый метод contains есть только в C++20
  char command = 0;
  std::string value;

  while (std::cin >> command >> value) {
    if (command == '+') {
      std::cout << (table.insert(value).second ? "OK" : "FAIL") << std::endl;
    } else if (command == '?') {
      std::cout << (table.count(value) ? "OK" : "FAIL") << std::endl;
    } else if (command == '-') {
      std::cout << (table.erase(value) ? "OK" : "FAIL") << std::endl;
    }
  }
  return 0;
}