Question

Write a Java program to implement Counting Sort and write a driver to test it. Note: use random number generator to generate your input with n = 10, 50, and 100. Verify that the running time is O(n).

Answer 1

import java.util.*;

class GFG

{

static void countSort(int[] arr)

{

  int max = Arrays.stream(arr).max().getAsInt();

int min = Arrays.stream(arr).min().getAsInt();

   int range = max - min + 1;

int count[] = new int[range];

   int output[] = new int[arr.length];

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

{

count[arr[i] - min]++;

}

for (int i = 1; i < count.length; i++)

{

count[i] += count[i - 1];

}

   for (int i = arr.length - 1; i >= 0; i--)

        {

            output[count[arr[i] - min] - 1] = arr[i];

            count[arr[i] - min]--;

        }

  

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

        {

            arr[i] = output[i];

        }

    }

static void printArray(int[] arr)

    {

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

        {

            System.out.print(arr[i] + " ");

        }

        System.out.println("Counting Sort");

    }

    // Driver code

    public static void main(String[] args)

    {

        int[] arr = {10, 50, 100};

        countSort(arr);

        printArray(arr);

    }

}

Points to be noted:

1. Counting sort is efficient if the range of input data is not significantly greater than the

number of objects to be sorted. Consider the situation where the input sequence is between

range 1 to 10 and the data is 10, 50, 100,

2. It is not a comparison based sorting. It running time complexity is O(n) with space

proportional to the range of data.

Counting Sort

Counting sort is a sorting technique based on keys between a specific range. It works by counting the number of objects

having distinct key values (kind of hashing). Then doing some arithmetic to calculate the position of each object in the output

sequence