目录
概述
源码
HashTable.h
UnorderedMap.h
UnorderedSet.h
test.cpp
STL标准模板库中的map、set的底层数据结构是红黑树,会在数据插入时自动排序,unordered_map、unordered_set的底层数据结构是哈希表,不做排序,根据哈希值进行映射。
哈希算法可见这篇文章:
【C++】哈希_种花家de小红帽的博客-CSDN博客
unordered_map、unordered_set的特性与map、set基本一样,数据插入和删除的效率都差不多,但是unordered_map、unordered_set的查询效率远高于map、set。
unordered_map、unordered_set的封装与map、set的封装很相似。
封装细节、迭代器设计具体可见这篇文章:
【C++】STL之map、set类源码剖析_种花家de小红帽的博客-CSDN博客
#pragma once
#include
#include
// 仿函数
template
struct HashFunc
{
size_t operator()(const K& key)
{
return (size_t)key;
}
};
// 特化
template<>
struct HashFunc
{
size_t operator()(const std::string& str)
{
size_t res = 0;
for (const auto& ch : str)
{
res *= 131; // 随机数取值,避免哈希冲突
res += ch;
}
return res;
}
};
// 节点
template
struct HashNode
{
T _data;
HashNode* next;
HashNode(const T& data)
: _data(data), next(nullptr)
{}
};
// 前置声明
template
class HashTable;
// 迭代器
template
struct Iterator
{
typedef HashNode Node;
typedef Iterator Self;
typedef HashTable HT;
Node* _node;
HT* _ht;
Iterator(Node* node, HT* ht)
: _node(node), _ht(ht)
{}
Ref operator*()
{
return _node->_data;
}
Ptr operator->()
{
return &_node->_data;
}
bool operator!=(const Self& s)const
{
return _node != s._node;
}
Self& operator++()
{
if (_node->next)
{
_node = _node->next;
}
else
{
// 寻找下一个桶的第一个节点
KofT kot;
Hash hs;
size_t pos = hs(kot(_node->_data)) % _ht->_table.size();
++pos;
while (pos < _ht->_table.size())
{
if (_ht->_table[pos] == nullptr)
{
++pos;
}
else
{
_node = _ht->_table[pos];
break;
}
}
if (pos == _ht->_table.size())
{
_node = nullptr;
}
}
return *this;
}
Self operator++(int)
{
Self tmp(*this);
++(*this);
return tmp;
}
};
// 哈希桶
template
class HashTable
{
typedef HashNode Node;
template
friend struct Iterator;
public:
typedef Iterator iterator;
typedef Iterator const_iterator;
iterator begin()
{
for (int i = 0; i < _table.size(); ++i)
{
if (_table[i] != nullptr)
{
return iterator(_table[i], this);
}
}
return iterator(nullptr, this);
}
iterator end()
{
return iterator(nullptr, this);
}
const_iterator begin()const
{
for (int i = 0; i < _table.size(); ++i)
{
if (_table[i] != nullptr)
{
return const_iterator(_table[i], this);
}
}
return const_iterator(nullptr, this);
}
const_iterator end()const
{
return const_iterator(nullptr, this);
}
// 迭代器拷贝构造
template
HashTable(InputIterator first, InputIterator last)
{
_n = 0;
_table.resize(10);
while (first != last)
{
insert(*first);
++first;
}
}
void swap(HashTable& ht)
{
std::swap(_table, ht._table);
std::swap(_n, ht._n);
}
HashTable(const HashTable& ht)
{
HashTable tmp(ht.begin(), ht.end());
swap(tmp);
}
HashTable& operator=(HashTable ht)
{
swap(ht);
return *this;
}
HashTable()
: _n(0)
{
_table.resize(10, nullptr);
}
~HashTable()
{
for (int i = 0; i < _table.size(); ++i)
{
Node* cur = _table[i];
while (cur)
{
Node* next = cur->next;
delete cur;
cur = next;
}
_table[i] = nullptr;
}
}
std::pair insert(const T& data)
{
KofT koft;
iterator it = find(koft(data));
if (it != end())
{
return std::make_pair(it, false);
}
// 扩容, 平衡因子为 1
if (_n == _table.size())
{
std::vector newTable;
newTable.resize(_table.size() * 2, nullptr);
for (int i = 0; i < _table.size(); ++i)
{
Node* cur = _table[i];
while (cur)
{
Node* next = cur->next;
size_t pos = Hash()(koft(cur->_data)) % newTable.size();
if (newTable[pos] == nullptr)
{
newTable[pos] = cur;
cur->next = nullptr;
}
else
{
cur->next = newTable[pos];
newTable[pos] = cur;
}
cur = next;
}
}
_table.swap(newTable);
}
// 插入节点
Node* newNode = new Node(data);
size_t pos = Hash()(koft(data)) % _table.size();
newNode->next = _table[pos];
_table[pos] = newNode;
++_n;
return std::make_pair(iterator(newNode, this), true);
}
iterator find(const K& key)
{
size_t pos = Hash()(key) % _table.size();
Node* cur = _table[pos];
while (cur)
{
if (KofT()(cur->_data) == key)
{
return iterator(cur, this);
}
cur = cur->next;
}
return iterator(nullptr, this);
}
bool erase(const K& key)
{
iterator it = find(key);
if (it != end())
{
size_t pos = Hash()(key) % _table.size();
Node* cur = _table[pos];
if (cur == it._node)
{
cur = it._node->next;
delete it._node;
it._node = nullptr;
}
else
{
while (cur->next != it._node)
{
cur = cur->next;
}
cur->next = it._node->next;
delete it._node;
it._node = nullptr;
}
--_n;
return true;
}
else
{
return false;
}
}
private:
std::vector _table;
size_t _n;
};
#pragma once
#include "HashTable.h"
template>
class UnorderedMap
{
struct MapKofT
{
const K& operator()(const std::pair& kv)
{
return kv.first;
}
};
public:
typedef typename HashTable, Hash, MapKofT>::iterator iterator;
typedef typename HashTable, Hash, MapKofT>::const_iterator const_iterator;
iterator begin()
{
return _ht.begin();
}
iterator end()
{
return _ht.end();
}
const_iterator begin()const
{
return _ht.begin();
}
const_iterator end()const
{
return _ht.end();
}
// 迭代器构造
template
UnorderedMap(InputIterator first, InputIterator last)
{
_ht = HashTable, Hash, MapKofT>(first, last);
}
UnorderedMap(UnorderedMap& uMap)
{
_ht = HashTable, Hash, MapKofT>(uMap.begin(), uMap.end());
}
UnorderedMap& operator=(UnorderedMap& uMap)
{
_ht = HashTable, Hash, MapKofT>(uMap.begin(), uMap.end());
return *this;
}
UnorderedMap()
: _ht(HashTable, Hash, MapKofT>())
{}
std::pair insert(const std::pair& kv)
{
return _ht.insert(kv);
}
iterator find(const K& key)
{
return _ht.find(key);
}
bool erase(const K& key)
{
return _ht.erase(key);
}
V& operator[](const K& key)
{
std::pair ret = _ht.insert(std::make_pair(key, V()));
return ret.first->second;
}
private:
HashTable, Hash, MapKofT> _ht;
};
#pragma once
#include "HashTable.h"
template>
class UnorderedSet
{
struct SetKofT
{
const K& operator()(const K& key)
{
return key;
}
};
public:
typedef typename HashTable::iterator iterator;
typedef typename HashTable::const_iterator const_iterator;
iterator begin()
{
return _ht.begin();
}
iterator end()
{
return _ht.end();
}
const_iterator begin()const
{
return _ht.begin();
}
const_iterator end()const
{
return _ht.end();
}
// 迭代器构造
template
UnorderedSet(InputIterator first, InputIterator last)
{
_ht = HashTable(first, last);
}
UnorderedSet(UnorderedSet& uSet)
{
_ht = HashTable(uSet.begin(), uSet.end());
}
UnorderedSet& operator=(UnorderedSet& uSet)
{
_ht = HashTable(uSet.begin(), uSet.end());
return *this;
}
UnorderedSet()
: _ht(HashTable())
{}
std::pair insert(const K& key)
{
std::pair ret = _ht.insert(key);
return std::make_pair(ret.first, ret.second);
}
iterator find(const K& key)
{
return _ht.find(key);
}
bool erase(const K& key)
{
return _ht.erase(key);
}
private:
HashTable _ht;
};
#include "UnorderedMap.h"
#include "UnorderedSet.h"
#include
using namespace std;
void unordered_map_test1()
{
int arr[] = { 34, 36, 12, 54, 5, 22, 65, 32, 13, 4, 1, 52 };
cout << "uMap1:" << endl;
UnorderedMap uMap1;
for (const auto& e : arr)
{
uMap1.insert(make_pair(e, e));
}
for (const auto& e : uMap1)
{
cout << e.first << ": " << e.second << endl;
}
cout << endl;
cout << uMap1.find(32)._node << endl;
cout << uMap1.find(42)._node << endl;
cout << uMap1.find(52)._node << endl;
uMap1.erase(32);
cout << uMap1.find(32)._node << endl;
cout << uMap1.find(42)._node << endl;
cout << uMap1.find(52)._node << endl;
UnorderedMap::iterator it1 = uMap1.begin();
while (it1 != uMap1.end())
{
cout << it1._node->_data.first << ": " << it1._node->_data.second << endl;
++it1;
}
cout << endl;
// 迭代器构造
cout << "uMap2:" << endl;
UnorderedMap uMap2(uMap1.begin(), uMap1.end());
UnorderedMap::iterator it2 = uMap2.begin();
while (it2 != uMap2.end())
{
cout << (*it2).first << ": " << (*it2).second << endl;
++it2;
}
cout << endl;
// 拷贝构造
cout << "uMap3:" << endl;
UnorderedMap uMap3(uMap2);
UnorderedMap::iterator it3 = uMap3.begin();
while (it3 != uMap3.end())
{
cout << (*it3).first << ": " << (*it3).second << endl;
it3++;
}
cout << endl;
}
void unordered_map_test2()
{
std::vector food = {
"蛋糕", "西瓜", "啤酒", "苹果", "香蕉", "蛋糕", "牛肉",
"西瓜", "苹果", "啤酒", "西瓜", "牛肉", "蛋糕", "蛋糕",
"西瓜", "西瓜", "牛肉", "苹果", "香蕉", "蛋糕", "西瓜"
};
UnorderedMap foodMap;
for (auto& e : food)
{
foodMap[e]++;
}
for (auto& e : foodMap)
{
std::cout << e.first << ": " << e.second << std::endl;
}
std::cout << std::endl;
}
void unordered_set_test()
{
int arr[] = { 34, 36, 12, 54, 5, 22, 65, 32, 13, 4, 1, 52 };
cout << "uSet1:" << endl;
UnorderedSet uSet1;
for (const auto& e : arr)
{
uSet1.insert(e);
}
for (auto& e : uSet1)
{
cout << e << ' ';
}
cout << endl;
cout << "uSet2:" << endl;
UnorderedSet uSet2(uSet1.begin(), uSet1.end());
for (auto& e : uSet2)
{
cout << e << ' ';
}
cout << endl;
cout << "uSet3:" << endl;
UnorderedSet uSet3(uSet2);
UnorderedSet::iterator it3 = uSet3.begin();
while (it3 != uSet3.end())
{
cout << *it3 << ' ';
++it3;
}
cout << endl;
}
int main()
{
unordered_map_test1();
unordered_map_test2();
unordered_set_test();
return 0;
}