Table of Contents

- 1 Why prime number is used in hashing?
- 2 What can be the value of M in H K K mod M division method )?
- 3 How is mod calculated in hash function?
- 4 Which of the following is the best choice as M in the hash function?
- 5 What is simple hash function?
- 6 Why is mod used in hashing?
- 7 Why do we use primes in hashing functions?
- 8 How do you hash a value with a non-prime?

## Why prime number is used in hashing?

Primes are used because you have good chances of obtaining a unique value for a typical hash-function which uses polynomials modulo P. Say, you use such hash-function for strings of length <= N, and you have a collision. That means that 2 different polynomials produce the same value modulo P.

## What can be the value of M in H K K mod M division method )?

Explanation: The value of m can be simply in powers of 2 since we can easily implement the function in most computers. m=2p where p is an integer.

**What is M in hash function?**

A universal hashing scheme is a randomized algorithm that selects a hashing function h among a family of such functions, in such a way that the probability of a collision of any two distinct keys is 1/m, where m is the number of distinct hash values desired—independently of the two keys.

### How is mod calculated in hash function?

With modular hashing, the hash function is simply h(k) = k mod m for some m (usually, the number of buckets). The value k is an integer hash code generated from the key. If m is a power of two (i.e., m=2p), then h(k) is just the p lowest-order bits of k.

### Which of the following is the best choice as M in the hash function?

A prime not too close to an exact power of 2 is often a good choice for m.

**What is the hash function used in the division?**

h(k) = m mod k.

#### What is simple hash function?

What is a Hash Function? A function that converts a given big phone number to a small practical integer value. The mapped integer value is used as an index in the hash table. In simple terms, a hash function maps a big number or string to a small integer that can be used as the index in the hash table.

#### Why is mod used in hashing?

Usually the modulo operator is used as the last step in selecting the bucket. The modulo operator is far from ideal, but it is good enough. It guarantees that the resulting hash bucket is in range: the result of key \% num_buckets is always in range of 0.. (num_buckets-1).

**What is H(K) in hash table?**

Here, h (k) is the hash value obtained by dividing the key value k by size of hash table n using the remainder. It is best that n is a prime number as that makes sure the keys are distributed with more uniformity.

## Why do we use primes in hashing functions?

This property is used in hashing functions. Given a string “Samuel”, you can generate a unique hash by multiply each of the constituent digits or letters with a prime number and adding them up. This is why primes are used. However using primes is an old technique.

## How do you hash a value with a non-prime?

$$ H = k \\bmod \\ 11$$ Now all the values will be placed one after another in 9 rows. For example, in the first bucket there will be $0, 11, 22 \\dots$. In the second, there will be $1, 12, 23 \\dots$ etc. Let’s say I decided to be a bad boy and use a non-prime as my hashing function – take 12. Using the Hashing function $$ H = k \\bmod \\ 12$$

**How to calculate hashCode of a given key?**

Here are 2 ‘statements’ that you most probably have read somewhere If you use a power of 2 for table_length, finding (hashCode (key) \% 2^n ) is as simple and quick as (hashCode (key) & (2^n -1)). But if your function to calculate hashCode for a given key isn’t good, you will definitely suffer from clustering of many keys in a few hash buckets.