C++哈希表封装实战指南

在C++中，可以使用哈希表（通常通过链表法解决冲突）封装unordered_set和unordered_map。以下是核心实现步骤和代码示例：

1. 哈希表基础结构

哈希节点模板（支持键值对）：

template <typename K, typename V>
struct HashNode {
K key;
V value;
HashNode* next;
HashNode(const K& k, const V& v) : key(k), value(v), next(nullptr) {}
};

桶数组与哈希函数：

template <typename K>
struct DefaultHashFunc {
size_t operator()(const K& key) const {
return std::hash<K>()(key);
}
};

2. 封装unordered_set

核心结构：

template <typename K, typename Hash = DefaultHashFunc<K>>
class UnorderedSet {
private:
std::vector<HashNode<K, K>*> buckets; // 存储节点指针
size_t bucket_count = 10; // 初始桶数量
Hash hash_func; // 哈希函数对象

// 获取桶索引
size_t get_bucket_index(const K& key) const {
return hash_func(key) % bucket_count;
}

public:
// 插入元素
void insert(const K& key) {
size_t index = get_bucket_index(key);
HashNode<K, K>* node = buckets[index];
while (node) {
if (node->key == key) return; // 已存在
node = node->next;
}
auto* new_node = new HashNode<K, K>(key, key);
new_node->next = buckets[index];
buckets[index] = new_node;
}
};

3. 封装unordered_map

修改节点与接口：

template <typename K, typename V, typename Hash = DefaultHashFunc<K>>
class UnorderedMap {
private:
std::vector<HashNode<K, V>*> buckets;
// … 其他与set类似

public:
// 插入键值对
void insert(const K& key, const V& value) {
size_t index = get_bucket_index(key);
HashNode<K, V>* node = buckets[index];
while (node) {
if (node->key == key) {
node->value = value; // 更新值
return;
}
node = node->next;
}
auto* new_node = new HashNode<K, V>(key, value);
new_node->next = buckets[index];
buckets[index] = new_node;
}

// 重载[]运算符
V& operator[](const K& key) {
size_t index = get_bucket_index(key);
HashNode<K, V>* node = buckets[index];
while (node) {
if (node->key == key) return node->value;
node = node->next;
}
// 若不存在，插入默认值
insert(key, V());
return buckets[index]->value;
}
};

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4. 迭代器实现（以unordered_map为例）

迭代器类：

template <typename K, typename V>
class UnorderedMapIterator {
private:
std::vector<HashNode<K, V>*>& buckets;
size_t bucket_index;
HashNode<K, V>* current;

// 找到下一个非空桶
void find_next() {
while (bucket_index < buckets.size() && !current) {
bucket_index++;
if (bucket_index < buckets.size()) current = buckets[bucket_index];
}
}

public:
UnorderedMapIterator(std::vector<HashNode<K, V>*>& b, size_t idx, HashNode<K, V>* node)
: buckets(b), bucket_index(idx), current(node) {
find_next();
}

// 重载++运算符
UnorderedMapIterator& operator++() {
if (current) current = current->next;
if (!current) {
bucket_index++;
find_next();
}
return *this;
}

// 重载*运算符
std::pair<K, V> operator*() const {
return {current->key, current->value};
}
};

5. 完整示例调用

int main() {
UnorderedMap<std::string, int> map;
map.insert("one", 1);
map["two"] = 2; // 使用[]插入

// 遍历输出
for (auto it = map.begin(); it != map.end(); ++it) {
std::cout << (*it).first << ": " << (*it).second << std::endl;
}
return 0;
}

关键优化方向：

通过以上结构，可灵活扩展为类似STL的哈希容器实现。