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

// Copyright 2020 Arctic2333
#include <stdlib.h>
#include<stdio.h>
#define MAX 6  // Determines how much data
# define HASHMAX 5  // Determines the length of the hash table
/**
  * Hash Search Algorithm
  * Best Time Complexity Ω(1)
  * 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. */
int data[MAX] = { 1, 10, 15, 5, 8, 7};  // test data
typedef struct list {
    int key;
    struct list * next;
}
node, * link;
node hashtab[HASHMAX];
int counter = 1;
/* int h(int key)
 * Mode of hash detection :
 * Division method */
int h(int key) {
    return key % HASHMAX;
}
/* void create_list(int key)
 * The same after the remainder will be added after the same hash header
 * To avoid conflict, zipper method is used
 * Insert elements into the linked list in the header */
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)
 * Input the key to be searched, and get the hash header position through the H (int key) function,
 * then one-dimensional linear search.
 * If found @return element depth and number of searches
 * If not found @return -1 */
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 -> key);
        if (pointer -> key == key)
            return 1;
        else
            pointer = pointer -> next;
    }
    return 0;
}
int main() {
    link p;
    int key, index, i;  // Key is the value to be found
    index = 0;
    // You can write the input mode here
    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) {
        // You can write the input mode here
        // test key = 10
        key = 10;
        if (hash_search(key))
            printf("search time = %d\n", counter);
        else
            printf("no found!\n");
        key = -1;  // Exit test
        /* The test sample is returned as: data[0]:data[5]:data[15]:data[10]:search time = 3
         * The search is successful. There are 10 in this set of data */
    }
    return 0;
}