点击这里

哈希表是以关联方式存储数据的数据结构。 在哈希表中，数据以数组格式存储，其中每个数据值都有自己唯一的索引值。 如果我们知道所需数据的索引，则访问数据变得非常快。

用C实现 (Implementation in C)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#define SIZE 20
struct DataItem {
   int data;   
   int key;
};
struct DataItem* hashArray[SIZE]; 
struct DataItem* dummyItem;
struct DataItem* item;
int hashCode(int key) {
   return key % SIZE;
}
struct DataItem *search(int key) {
   //get the hash 
   int hashIndex = hashCode(key);  
   //move in array until an empty 
   while(hashArray[hashIndex] != NULL) {
      if(hashArray[hashIndex]->key == key)
         return hashArray[hashIndex]; 
      //go to next cell
      ++hashIndex;
      //wrap around the table
      hashIndex %= SIZE;
   }        
   return NULL;        
}
void insert(int key,int data) {
   struct DataItem *item = (struct DataItem*) malloc(sizeof(struct DataItem));
   item->data = data;  
   item->key = key;
   //get the hash 
   int hashIndex = hashCode(key);
   //move in array until an empty or deleted cell
   while(hashArray[hashIndex] != NULL && hashArray[hashIndex]->key != -1) {
      //go to next cell
      ++hashIndex;
      //wrap around the table
      hashIndex %= SIZE;
   }
   hashArray[hashIndex] = item;
}
struct DataItem* delete(struct DataItem* item) {
   int key = item->key;
   //get the hash 
   int hashIndex = hashCode(key);
   //move in array until an empty
   while(hashArray[hashIndex] != NULL) {
      if(hashArray[hashIndex]->key == key) {
         struct DataItem* temp = hashArray[hashIndex]; 
         //assign a dummy item at deleted position
         hashArray[hashIndex] = dummyItem; 
         return temp;
      }
      //go to next cell
      ++hashIndex;
      //wrap around the table
      hashIndex %= SIZE;
   }      
   return NULL;        
}
void display() {
   int i = 0;
   for(i = 0; i<SIZE; i++) {
      if(hashArray[i] != NULL)
         printf(" (%d,%d)",hashArray[i]->key,hashArray[i]->data);
      else
         printf(" ~~ ");
   }
   printf("\n");
}
int main() {
   dummyItem = (struct DataItem*) malloc(sizeof(struct DataItem));
   dummyItem->data = -1;  
   dummyItem->key = -1; 
   insert(1, 20);
   insert(2, 70);
   insert(42, 80);
   insert(4, 25);
   insert(12, 44);
   insert(14, 32);
   insert(17, 11);
   insert(13, 78);
   insert(37, 97);
   display();
   item = search(37);
   if(item != NULL) {
      printf("Element found: %d\n", item->data);
   } else {
      printf("Element not found\n");
   }
   delete(item);
   item = search(37);
   if(item != NULL) {
      printf("Element found: %d\n", item->data);
   } else {
      printf("Element not found\n");
   }
}

如果我们编译并运行上面的程序，它将产生以下结果 -

输出 (Output)

 ~~  (1,20)  (2,70)  (42,80)  (4,25)  ~~  ~~  ~~  ~~  ~~  ~~  ~~ (12,44)  (13,78)  (14,32)  ~~  ~~  (17,11)  (37,97)  ~~ 
Element found: 97
Element not found