C语言手撕一个Hash表(HashTable)实例代码

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>

typedef struct node {
    int key;
    int val;
    struct Node *next;
} Node;

typedef struct HashMap {
    int size;
    int count;
    struct Node **hashmap;
} HashMap;

// 定义哈希函数
unsigned int hash(int n) {
    return (unsigned int) n;
}

// 创建一个节点
Node *creatNode(int key, int val) {
    Node *node = (Node *) malloc(sizeof(Node));
    node->key = key;
    node->val = val;
    node->next = NULL;
    return node;
}

// 创建一个hash表
HashMap *createHashMap() {
    HashMap *H = (HashMap *) malloc(sizeof(HashMap));
    H->size = 8;
    H->count = 0;
    H->hashmap = (Node **) calloc(H->size, sizeof(Node *));
    return H;
}

// 扩容，以2倍的形式扩容
static void extend(HashMap *map) {
    int newsize = map->size * 2;
    Node **newhashmap = (Node **) calloc(newsize, sizeof(Node *));
    for (int i = 0; i < map->size; i++) {
        Node *node = map->hashmap[i];
        Node *head1 = (Node *) malloc(sizeof(Node));
        Node *head2 = (Node *) malloc(sizeof(Node));
        Node *temp1 = head1;
        Node *temp2 = head2;
        while (node) {
            if (hash(node->key) % newsize != i) {
                temp2->next = node;
                temp2 = temp2->next;
            } else {
                temp1->next = node;
                temp1 = temp1->next;
            }
            node = node->next;
        }
        temp1->next = NULL;
        temp2->next = NULL;
        newhashmap[i] = head1->next;
        newhashmap[i + map->size] = head2->next;
        free(head1);
        free(head2);
    }
    map->size = newsize;
    free(map->hashmap);
    map->hashmap = newhashmap;
}

// 插入某个结点
bool insert(HashMap *map, int key, int val) {
    int hash_key = hash(key) % map->size;
    // 要插入的哈希值未产生碰撞
    if (map->hashmap[hash_key] == NULL) {
        map->count++;
        map->hashmap[hash_key] = creatNode(key, val);
    } else {
        Node *head = map->hashmap[hash_key];
        if (head->key == key) return false;
        while (head->next && head->next->key != key) head = head->next;
        if (head->next == NULL) {
            map->count++;
            head->next = creatNode(key, val);
        } else if (head->next->key == key) return false;
    }
	// 装载因子过高就开始扩容
    if (map->count / map->size > 0.75) extend(map);
    return true;
}

// 寻找某个结点
bool find(HashMap *map, int key, int *v) {
    int hash_key = hash(key) % map->size;
    if (map->hashmap[hash_key] == NULL) {
        return false;
    } else {
        Node *head = map->hashmap[hash_key];
        if (head->key == key) {
            *v = head->val;
            return true;
        }
        while (head->next && head->next->key != key) head = head->next;
        if (head->next == NULL) return false;
        if (head->next->key == key) {
            *v = head->next->val;
            return true;
        }
    }
    return false;
}

// 删除某个结点
void delete(HashMap *map, int key) {
    int hash_key = hash(key) % map->size;
    if (map->hashmap[hash_key] == NULL) return;
    Node *head = map->hashmap[hash_key];
    if (head->key == key) {
        map->hashmap[hash_key] = head->next;
        map->count--;
        free(head);
        return;
    }
    while (head->next && head->next->key != key) head = head->next;
    if (head->next == NULL) return;
    if (head->next->key == key) {
        Node *temp = head->next;
        head->next = head->next->next;
        map->count--;
        free(temp);
    }
    return;
}


int main() {
    HashMap *H = createHashMap();
    for (int i = 0; i < 1024; i++) {
        insert(H, i, i);
    }
    printf("H size is %d\n",H->size);
    printf("H count is %d\n",H->count);
    delete(H, 0);
    int v = 0;
    if (find(H, 0, &v)) printf("%d\n", v);
    else printf("not find \n");
    if (find(H, 4, &v)) printf("%d\n", v);
    else printf("not find \n");
    return 0;
}