Frequency Array

How frequency array works and created

Introduction

In many problems, we need to count how many times each value appears in an array or a string. A frequency array is an auxiliary array freq[] where:

• the index represents a value (or an encoded value, such as a character);
• the element at that index stores how many times that value occurs.

For example, if the input array is $a = [1, 2, 1, 3, 2, 1, 1]$, then:

A frequency array is especially useful when the range of possible values is small and known in advance.

Example 1: Counting Frequencies of Numbers

Given integers $N$ and $M$, and an array of integers where , print how many times each number appears.