哈希表就是鍵值key-value對，使用hash函數讓key產生哈希值，當不同的key產生相同的哈希值時就是哈希沖突了，產生哈希沖突可以使用拉鏈法。

hash.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "hash.h"static unsigned int table_size[] = {
7, 13, 31, 61, 127, 251, 509, 1021, 2039, 4093, 8191,
16381, 32749, 65521, 131071,
262143, 524287, 1048575, 2097151, 4194303, 8388607,
16777211, 33554431, 67108863, 134217727, 268435455,
536870911, 1073741823, 2147483647, 0};/* hash function: return unsignde int */
static unsigned int hash(const char *key)
{unsigned int seed = 131;unsigned int hash = 0;while (*key) {hash = hash * seed + (*key++);}return (hash & 0x7FFFFFFF) % SIZE;
}void hash_insert(struct hash_table *ht, char *key, char *value)
{unsigned int h;struct hash_node *node,*pnode,*fnode;node=pnode=(struct hash_node *)malloc(sizeof(struct hash_node));fnode=(struct hash_node *)malloc(sizeof(struct hash_node));memset(node,0,sizeof(struct hash_node));node->next=NULL;memset(fnode,0,sizeof(struct hash_node));fnode->next=NULL;h = hash(key);if(ht[h].ht==0){ht[h].ht=fnode;}pnode=ht[h].ht;while(pnode->next!=NULL){pnode=pnode->next;}pnode->key=key;pnode->value=value;pnode->next=node;
}char* search(struct hash_table *ht, char *key)
{unsigned int h;struct hash_node *pnode;char *ret=(char*)malloc(sizeof(char));pnode=(struct hash_node *)malloc(sizeof(struct hash_node));h = hash(key);if(ht[h].ht==0){return ret=NULL;}else{pnode=ht[h].ht;while(pnode->next!=NULL&&pnode->key!=key){pnode=pnode->next;}if(pnode->key==key){return ret=pnode->value;}else{return ret=NULL;}}
}int main() {int i;char *a1;char *a2;char *search_key;char *search_ret;struct hash_table *h;struct hash_node *node;h=(struct hash_table *)malloc(sizeof(struct hash_table)*SIZE);memset(h,0,sizeof(struct hash_table)*SIZE);/*for(i=0;i<SIZE;i++){node=(struct hash_node *)malloc(sizeof(struct hash_node));memset(node,0,sizeof(struct hash_node));node->next=NULL;h[i].ht=node;}*/a1="aaa";a2="abc";hash_insert(h,a1,a2);a1="bbb";a2="jkjhk";hash_insert(h,a1,a2);a1="ccc";a2="reew";hash_insert(h,a1,a2);a1="ddd";a2="hyte";hash_insert(h,a1,a2);a1="eee";a2="wwq";hash_insert(h,a1,a2);a1="fff";a2="fd4";hash_insert(h,a1,a2);search_key="dddd";search_ret=search(h,search_key);return 0;
}

另一種方法一開始就for循環初始化node

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "hash.h"static unsigned int table_size[] = {
7, 13, 31, 61, 127, 251, 509, 1021, 2039, 4093, 8191,
16381, 32749, 65521, 131071,
262143, 524287, 1048575, 2097151, 4194303, 8388607,
16777211, 33554431, 67108863, 134217727, 268435455,
536870911, 1073741823, 2147483647, 0};/* hash function: return unsignde int */
static unsigned int hash(const char *key)
{unsigned int seed = 131;unsigned int hash = 0;while (*key) {hash = hash * seed + (*key++);}return (hash & 0x7FFFFFFF) % SIZE;
}hash_insert(struct hash_table *ht, char *key, char *value)
{unsigned int h;struct hash_node *node,*pnode;node=pnode=(struct hash_node *)malloc(sizeof(struct hash_node));memset(node,0,sizeof(struct hash_node));node->next=NULL;h = hash(key);pnode=ht[h].ht;while(pnode->next!=NULL){pnode=pnode->next;}pnode->key=key;pnode->value=value;pnode->next=node;
}int main() {int i;char *a1;char *a2;struct hash_table *h=(struct hash_table *)malloc(sizeof(struct hash_table)*SIZE);struct hash_node *node=NULL;memset(h,0,sizeof(struct hash_table)*SIZE);for(i=0;i<SIZE;i++){node=(struct hash_node *)malloc(sizeof(struct hash_node));memset(node,0,sizeof(struct hash_node));node->next=NULL;h[i].ht=node;}a1="aaa";a2="abc";hash_insert(h,a1,a2);a1="bbb";a2="jkjhk";hash_insert(h,a1,a2);a1="ccc";a2="reew";hash_insert(h,a1,a2);a1="ddd";a2="hyte";hash_insert(h,a1,a2);a1="eee";a2="wwq";hash_insert(h,a1,a2);a1="fff";a2="fd4";hash_insert(h,a1,a2);return 0;
}

hash.h

struct hash_node{struct hash_node* next;char * key;char * value;
};struct hash_table{struct hash_node *ht;
};#define SIZE 1

SIZE就是哈希表數組的大小，現在故意設置其為1，則哈希表退化為普通鏈表，這里只是為了演示所有的數據應該鏈接在一起

擴大SIZE為5，因為我們有6對數據，所以必然最少會有2個數據沖突，沖突的放一起：

總結

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