HashMap Implementation from Scratch in DSA C - Build from Scratch

HashMap Implementation from Scratch

📖 Scenario: Imagine you are building a simple phone book application. You want to store names and their phone numbers so you can quickly find a number by a name. To do this efficiently, you will create your own HashMap from scratch in C.

🎯 Goal: Build a basic HashMap in C that can store key-value pairs (names and phone numbers), handle collisions using chaining, and allow insertion and lookup operations.

📋 What You'll Learn

Create a struct for HashMap entries with key and value

Create a HashMap struct with an array of pointers for buckets

Implement a simple hash function for strings

Implement insert and search functions

Handle collisions using linked lists (chaining)

Print the phone number for a given name

💡 Why This Matters

🌍 Real World

HashMaps are used in many applications like phone books, caches, and databases to quickly find data by keys.

💼 Career

Understanding how HashMaps work internally helps in optimizing software and solving problems efficiently in software development roles.

1

Create the basic data structures

Create a struct called Entry with char key[50], char value[15], and a pointer next to another Entry. Then create a struct called HashMap with an array buckets of size 10 holding pointers to Entry.

DSA C

// Your code here for struct Entry and struct HashMap

Hint

Think of Entry as a node in a linked list holding a name and phone number. The HashMap holds an array of these lists.

2

Add a hash function and initialize the HashMap

Add a function int hash(char* key) that returns the sum of ASCII values of characters in key modulo 10. Also, write a function void initHashMap(HashMap* map) that sets all buckets pointers to NULL.

DSA C

// Your code here for hash function and initHashMap function

Hint

The hash function converts a string to an index between 0 and 9. Initializing sets all bucket pointers to NULL.

3

Implement insert and search functions

Write a function void insert(HashMap* map, char* key, char* value) that adds a new Entry to the correct bucket using chaining. Also write char* search(HashMap* map, char* key) that returns the value for the given key or NULL if not found.

DSA C

// Your code here for insert and search functions

Hint

Insert adds new entries at the start of the linked list for the bucket. Search walks through the list to find the key.

4

Test the HashMap by inserting and searching

In main(), create a HashMap variable called phoneBook. Initialize it using initHashMap. Insert these entries: ("Alice", "12345"), ("Bob", "67890"), ("Charlie", "54321"). Then print the phone number for "Bob" using search.

DSA C

int main() {
    // Your code here to create, initialize, insert, and print
    return 0;
}

Hint

Use printf to display the phone number found by search. Remember to check if the result is NULL.