C Program To Implement Dictionary Using Hashing - Algorithms

The implementation above uses separate chaining—each bucket points to a linked list of entries. Alternatives include:

| Method | Pros | Cons | |--------|------|------| | Separate Chaining | Simple, handles high load, no clustering | Extra memory for pointers | | Linear Probing | Cache-friendly, no pointers | Primary clustering, deletion complex | | Quadratic Probing | Reduces primary clustering | Secondary clustering | | Double Hashing | Excellent distribution | More computation |

For most general-purpose dictionaries, separate chaining is recommended due to its simplicity and predictable performance.

Our implementation will consist of four critical components: c program to implement dictionary using hashing algorithms

Let’s build each component step by step.

Resizing involves creating a new larger bucket array, rehashing all entries, and freeing the old structure.

void resize_dictionary(Dictionary *dict) 
    unsigned long old_size = dict->size;
    Entry **old_buckets = dict->buckets;
// Double the size
dict->size *= 2;
dict->buckets = (Entry**)calloc(dict->size, sizeof(Entry*));
dict->count = 0; // Will be rebuilt
// Rehash all entries
for (unsigned long i = 0; i < old_size; i++) 
    Entry *curr = old_buckets[i];
    while (curr) 
        Entry *next = curr->next;
        unsigned long new_index = dict->hash_func(curr->key) % dict->size;
        curr->next = dict->buckets[new_index];
        dict->buckets[new_index] = curr;
        dict->count++;
        curr = next;
free(old_buckets);

In the realm of computer science, a dictionary (also known as a map, symbol table, or associative array) is one of the most fundamental and versatile data structures. It allows you to store key-value pairs and retrieve values in near-constant time, regardless of the size of the data. While languages like Python, Java, and C++ have built-in dictionary implementations (e.g., dict, HashMap, std::unordered_map), the C programming language does not provide a standard one. This forces C developers to implement their own dictionary from scratch.

The most efficient way to implement a dictionary in C is by using hashing algorithms. This article provides an exhaustive guide to building a robust dictionary using hashing, covering everything from the theory of hash functions to collision resolution strategies, complete with a fully functional C implementation. Let’s build each component step by step

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define TABLE_SIZE 101
// A key-value pair node
typedef struct Entry 
char* key;
int value;
struct Entry* next;
 Entry;
// Dictionary structure
typedef struct 
Entry** buckets;
int size;      // number of buckets (table size)
int count;     // number of key-value pairs stored
 Dictionary;
 Resizing involves creating a new larger bucket array,