TheAlgorithms-C-Plus-Plus/search/hash_search.cpp

// Copyright 2020 Arctic2333
#include <stdlib.h>
#include<stdio.h>
#define MAX 6
# define HASHMAX 5
// Hash Search Algorithm
// Best Time Complexity Ω(1)
int data[MAX] = { 12, 160, 219, 522, 725, 9997};
typedef struct list {
    int key;
    struct list * next;
}
node, * link;
node hashtab[HASHMAX];
int counter = 1;
int h(int key) {
    return key % HASHMAX;
}
/* In this algorithm, we use the method of division and reservation remainder to construct the hash function, 
   and use the method of chain address to solve the conflict, that is, we link a chain list after the data, 
   and store all the records whose keywords are synonyms in the same linear chain list. */
void create_list(int key) {  // Construct hash table
    link p, n;
    int index;
    n = (link) malloc(sizeof(node));
    n -> key = key;
    n -> next = NULL;
    index = h(key);
    p = hashtab[index].next;
    if (p != NULL) {
        n -> next = p;
        hashtab[index].next = n;
    } else {
        hashtab[index].next = n; }
}
int hash_search(int key) {  // Hash lookup function
    link pointer;
    int index;
    counter = 0;
    index = h(key);
    pointer = hashtab[index].next;
    printf("data[%d]:", index);
    while (pointer != NULL) {
        counter++;
        printf("data[%d]:", pointer -> next);
        if (pointer -> key == key)
            return 1;
        else
            pointer = pointer -> next;
    }
    return 0;
}
int main() {
    link p;
    int key, index, i;
    index = 0;
    printf("input data:");
    for (i = 0; i < HASHMAX; i++)
        scanf("%d", & data[i]);
    printf("\n");
    while (index < MAX) {  // Construct hash table
        create_list(data[index]);
        index++;
    }
    for (i = 0; i < HASHMAX; i++) {  // Output hash table
        printf("hashtab [%d]", i);
        printf("n");
        p = hashtab[i].next;
        while (p != NULL) {
            printf("please int key:");
            if (p -> key > 0)
                printf("[%d]", p -> key);
            p = p -> next;
        }
        printf("\n");
    }
    while (key != -1) {
        printf("please input data\n");
        scanf("%d", & key);
        if (hash_search(key))
            printf("search time = %d\n", counter);
        else
            printf("no found!\n");
    }
    return 0;
}