hash_table_separate_chaining

#include <iostream>
#include <vector>
#include <forward_list>
#include <string>

class HashTable
{
public:
    HashTable();
    HashTable(size_t base, size_t startCapacity);
    bool Add(const std::string &value);
    bool Find(const std::string &value);
    bool Delete(const std::string &value);
private:
    std::vector <std::forward_list<std::string>> hash_table;
    size_t hash_base;
    size_t size;
    size_t hash(const std::string &value);
    void rehash();
};

HashTable::HashTable(size_t base, size_t startCapacity) : hash_table(startCapacity), hash_base(base), size(0)
{}

void HashTable::rehash()
{
    auto old_data(std::move(hash_table));
    hash_table.clear();
    hash_table.resize(old_data.size() * 2);
    for (auto& i : old_data)
        for (auto j = i.begin(); j != i.end(); ++j)
            Add(*j);
}

size_t HashTable::hash(const std::string& value)
{
    size_t ans = 1;
    for (size_t i = 0; i < value.size(); i++)
        ans = (static_cast<size_t>(value[i]) + ans) * hash_base;
    return ans;
}

bool HashTable::Add(const std::string& value)
{
    if (Find(value))
        return false;
    size_t key = hash(value) % hash_table.size();
    hash_table[key].push_front(value);
    size++;
    if (size >= 2 * hash_table.size())
        rehash();
    return true;
}

bool HashTable::Find(const std::string& value)
{
    size_t key = hash(value) % hash_table.size();
    for (auto i = hash_table[key].begin(); i != hash_table[key].end(); ++i)
    {
        if (value.compare(*i) == 0)
            return true;
    }
    return false;
}

bool HashTable::Delete(const std::string& value)
{
    if (!Find(value))
        return false;
    size_t key = hash(value) % hash_table.size();
    hash_table[key].remove(value);
    return true;
}

void result(bool res)
{
    if (res)
        std::cout << "OK\n";
    else
        std::cout << "FAIL\n";
}

int main()
{
    size_t N = 8;
    HashTable h(3, N);
    char operation;
    std::string str;
    while (std::cin)
    {
        std::cin >> operation >> str;
        if (operation == '+')
            result(h.Add(str));
        else if (operation == '-')
            result(h.Delete(str));
        else
            result(h.Find(str));
    }
    return 0;
}