Hash Functions

Hash functions play a crucial role in the functionality of hash tables. A hash function is an algorithm that takes an input (or a key) and returns a fixed-size numerical value, which is typically used as an index for storing or retrieving data from a hash table.

A good hash function should have the following properties:

• Deterministic: Given the same input, the hash function should always produce the same output.
• Uniform Distribution: The hash values should be uniformly distributed across the range of possible outputs.
• Minimize Collisions: Collisions occur when two different inputs produce the same hash value. A good hash function should minimize the likelihood of collisions.

Hash functions are designed to operate efficiently on different types of input data, such as strings, integers, or objects.

Let's take a look at an example of a simple hash function in Java:

1class HashFunction {
2  private int size;
3
4  public HashFunction(int size) {
5    this.size = size;
6  }
7
8  public int hash(String key) {
9    int hashValue = 0;
10    for (int i = 0; i < key.length(); i++) {
11      hashValue += key.charAt(i);
12    }
13    return hashValue % size;
14  }
15}
16
17// Example usage
18HashFunction hashFunction = new HashFunction(10);
19int hashCode = hashFunction.hash("example");
20System.out.println("Hash code: " + hashCode);

In this example, we define a HashFunction class that uses the sum of the character values in a string as the hash value. The hash method takes a key as input and returns the hash code by summing the character values and modulo dividing it by the size of the hash table.

For example, if we create an instance of the HashFunction class with a size of 10 and call hash("example"), it will calculate the hash value of the string "example" and return the hash code.

Hash functions are a fundamental concept in hash tables, and understanding how they work is essential for efficient data retrieval and storage in hash tables.

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class HashFunction {

  private int size;

​

  public HashFunction(int size) {

    this.size = size;

  }

​

  public int hash(String key) {

    int hashValue = 0;

    for (int i = 0; i < key.length(); i++) {

      hashValue += key.charAt(i);

    }

    return hashValue % size;

  }

}

​

// Example usage

HashFunction hashFunction = new HashFunction(10);

int hashCode = hashFunction.hash("example");

System.out.println("Hash code: " + hashCode);