What Is Hashing In C

Hashing serves multiple purposes. Initially, it aids in minimizing memory consumption for storing extensive datasets through data compression. Subsequently, it enhances algorithm efficiency by facilitating rapid data retrieval and search operations. Ultimately, it plays a crucial role in maintaining data integrity by identifying duplicate data and averting collisions, which occur when distinct keys are mapped to the same index.

The procedure of hashing consists of three primary stages: formulating the hash function, producing the hash value, and saving the information in the hash table.

Designing the hash function requires creating an algorithm that links the input data to a set-size output value. The goal is to evenly spread out the data in the hash table to minimize the chances of collisions. An effective hash function should also prioritize speed, simplicity, and determinism, meaning it consistently generates the same result for a given input.

After establishing the hash function, the subsequent task is to produce the hash value for the given data. This process entails running the data through the hash function, resulting in a consistent hash value of a specific size. Subsequently, this hash value is employed as an identifier within the hash table to retain the data.

Placing the information in the hash table requires placing it in the appropriate position in the array. Should a collision happen (meaning two distinct keys are assigned to the same index), the hash table can employ a method known as chaining to accommodate both keys at that index. Chaining involves establishing a linked list for each index and appending the keys to the linked list.

Hashing in C can be executed through various techniques, such as the division approach, multiplication approach, and the folding technique. The division method consists of calculating the remainder when the key is divided by the hash table's size to find the index. In the multiplication method, the key is multiplied by a fixed value, and the fractional part of the outcome is used to identify the index. The folding method, on the other hand, requires breaking down the key into segments, summing them up, and utilizing the total to ascertain the index.

Implementation of a hash table in C using arrays:

#include<stdio.h>
#define size 7
int array[size];
void init()
{   
    int i;
    for(i = 0; i < size; i++)
        array[i] = -1;
}

void insert(int val)
{   
    int key = val % size;
    
    if(array[key] == -1)
    {   
        array[key] = val;
        printf("%d inserted at array[%d]\n", val,key);
    }
    else
    {   
        printf("Collision : array[%d] has element %d already!\n",key,array[key]);
        printf("Unable to insert %d\n",val);
    }
}

void del(int val)
{
    int key = val % size;
    if(array[key] == val)
        array[key] = -1;
    else
        printf("%d not present in the hash table\n",val);
}

void search(int val)
{
    int key = val % size;
    if(array[key] == val)
        printf("Search Found\n");
    else
        printf("Search Not Found\n");
}

void print()
{
    int i;
    for(i = 0; i < size; i++)
        printf("array[%d] = %d\n",i,array[i]);
}

int main()
{
    init();
    insert(10); 
    insert(4);  
    insert(2);
    insert(3); 

    printf("Hash table\n");
    print();
    printf("\n");

    printf("Deleting value 10..\n");
    del(10);
    printf("After the deletion hash table\n");
    print();
    printf("\n");

    printf("Deleting value 5..\n");
    del(5);
    printf("After the deletion hash table\n");
    print();
    printf("\n");

    printf("Searching value 4..\n");
    search(4);
    printf("Searching value 10..\n");
    search(10);

    return 0;
}

Output

10 inserted at array[3]
4 inserted at array[4]
2 inserted at array[2]
Collision : array[3] has element 10 already!
Unable to insert 3
Hash table
array[0] = -1
array[1] = -1
array[2] = 2
array[3] = 10
array[4] = 4
array[5] = -1
array[6] = -1

Deleting value 10..
After the deletion hash table
array[0] = -1
array[1] = -1
array[2] = 2
array[3] = -1
array[4] = 4
array[5] = -1
array[6] = -1

Deleting value 5..
5 not present in the hash table
After the deletion hash table
array[0] = -1
array[1] = -1
array[2] = 2
array[3] = -1
array[4] = 4
array[5] = -1
array[6] = -1

Searching value 4..
Search Found
Searching value 10..
Search Not Found

Hashing serves as a method employed in computer programming for efficiently searching and fetching data from extensive datasets. Within the realm of C programming, hashing frequently finds application in constructing hash tables or associative arrays. Here are a few instances, benefits, and drawbacks of utilizing hashing in C:

Usage:

• ✅ Hashing can be used to implement efficient data lookup operations, such as searching for a specific value in a large array or table.
• ✅ Hashing can be used to implement data structures like hash tables, which provide constant-time lookup, insertion, and deletion operations.

Advantages:

• ✅ Hashing provides fast data retrieval and search times, making it useful for large datasets where performance is a concern.
• ✅ Hashing is relatively simple to implement in C and can be used to build complex data structures like hash tables or hash maps.
• ✅ Hashing can also be used for data security purposes, such as password storage or data encryption.

Disadvantages:

• ✅ Hashing collisions can occur, which can lead to reduced performance and longer search times.
• ✅ Hashing requires a good hash function that can evenly distribute the data across the hash table. Creating a good hash function can be challenging and time-consuming.
• ✅ Hashing can consume a lot of memory, especially if the hash table needs to store a large number of items or if the hash function has a high collision rate.

In essence, hashing serves as a valuable method for efficiently locating and accessing information within extensive datasets. However, it does encounter certain constraints like collisions, the necessity for a quality hash function, and significant memory usage.

Conclusion:

Hashing in C represents a potent method enabling effective search, retrieval, and comparison of information in extensive datasets. The process entails developing a hash function that translates input data into a predetermined hash value. This value serves as an index in a hash table where the data is stored. Through the utilization of hashing, developers can enhance algorithm efficiency and minimize the memory footprint needed to accommodate substantial datasets.