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#pragma once
#include <stdexcept>
#include <vector>
template <class Key, class Value, class Hash = std::hash<Key>>
class linear_probing_hashmap
{
private:
using pair_type = std::pair<Key, Value>;
struct node
{
pair_type data;
bool empty = true;
bool deleted = false;
// TODO: This might be wasteful.
node() = default;
node(const Key& key, const Value& value)
: data(std::make_pair(key, value))
{}
};
std::vector<node> _data;
Hash _hash;
double _load_factor;
size_t _size = 0;
size_t _jump_value = 1;
size_t get_hash_index(const Key& key) const
{
return _hash(key) % bucket_count();
}
void increment_index(size_t& index, size_t max_size) const
{
index += _jump_value;
// TODO: empty?
if (index >= max_size)
index %= max_size;
}
size_t get_iterations_needed() const
{
return _data.size();
}
public:
linear_probing_hashmap(size_t initial_capacity, double load_factor, size_t jump_value = 1)
: _data(initial_capacity)
, _load_factor(load_factor)
, _jump_value(jump_value)
{}
linear_probing_hashmap()
: linear_probing_hashmap(10, 0.75)
{}
void insert(const Key& key, const Value& value);
const Value& find(const Key& key) const;
Value& modify(const Key& key);
void erase(const Key& key);
void resize(size_t count);
size_t size() const
{
return _size;
}
bool empty() const
{
return _size == 0;
}
size_t bucket_count() const
{
return _data.size();
}
double max_load_factor() const
{
return _load_factor;
}
};
template <class Key, class Value, class Hash>
void linear_probing_hashmap<Key, Value, Hash>::insert(const Key& key, const Value& value)
{
size_t current_index = get_hash_index(key);
size_t iterations_needed = get_iterations_needed();
for (size_t i = 0; i < iterations_needed; i++)
{
node& current_node = _data[current_index];
// Element is contained in the collection.
if (!current_node.empty && !current_node.deleted && current_node.data.first == key)
{
current_node.data.second = value;
return;
}
// We don't need to check for deleted flag here.
if (current_node.empty)
{
current_node = node(key, value);
current_node.empty = false;
current_node.deleted = false;
++_size;
if (size() >= bucket_count() * max_load_factor())
{
resize(2 * bucket_count());
}
return;
}
increment_index(current_index, _data.size());
}
throw std::runtime_error("Numbers are not co-prime!");
}
template <class Key, class Value, class Hash>
const Value& linear_probing_hashmap<Key, Value, Hash>::find(const Key& key) const
{
size_t current_index = get_hash_index(key);
size_t iterations_needed = get_iterations_needed();
for (size_t i = 0; i < iterations_needed; i++)
{
const node& current_node = _data[current_index];
if (current_node.empty && !current_node.deleted)
{
break;
}
if (!current_node.empty && !current_node.deleted && current_node.data.first == key)
{
return current_node.data.second;
}
increment_index(current_index, _data.size());
}
throw std::out_of_range("[linear_probing_hashmap]: Element not found.");
}
template <class Key, class Value, class Hash>
Value& linear_probing_hashmap<Key, Value, Hash>::modify(const Key& key)
{
size_t current_index = get_hash_index(key);
size_t iterations_needed = get_iterations_needed();
for (size_t i = 0; i < iterations_needed; i++)
{
node& current_node = _data[current_index];
if (current_node.empty && !current_node.deleted)
{
break;
}
if (!current_node.empty && !current_node.deleted && current_node.data.first == key)
{
return current_node.data.second;
}
increment_index(current_index, _data.size());
}
throw std::out_of_range("[linear_probing_hashmap]: Element not found.");
}
template <class Key, class Value, class Hash>
void linear_probing_hashmap<Key, Value, Hash>::erase(const Key& key)
{
size_t current_index = get_hash_index(key);
size_t iterations_needed = get_iterations_needed();
for (size_t i = 0; i < iterations_needed; i++)
{
node& current_node = _data[current_index];
if (current_node.empty && !current_node.deleted)
{
break;
}
if (current_node.data.first == key)
{
current_node.deleted = true;
current_node.empty = true;
_size--;
break;
}
increment_index(current_index, _data.size());
}
}
template <class Key, class Value, class Hash>
void linear_probing_hashmap<Key, Value, Hash>::resize(size_t count)
{
// TODO: Ensure count is big enough.
std::vector<node> new_data(count);
for (const auto& current_element : _data)
{
if (current_element.empty)
continue;
size_t current_index = _hash(current_element.data.first) % new_data.size();
size_t iterations_needed = new_data.size();
for (size_t i = 0; i < iterations_needed; i++)
{
node& current_node = new_data[current_index];
if (current_node.empty)
{
current_node = current_element;
break;
}
increment_index(current_index, new_data.size());
}
}
_data = std::move(new_data);
}
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