Counting Sort 2 – HackerRank Solution

In this post, we will solve Counting Sort 2 HackerRank Solution. This problem (Counting Sort 2) is a part of HackerRank Problem Solving series.

Task

Often, when a list is sorted, the elements being sorted are just keys to other values. For example, if you are sorting files by their size, the sizes need to stay connected to their respective files. You cannot just take the size numbers and output them in order, you need to output all the required file information.

The counting sort is used if you just need to sort a list of integers. Rather than using a comparison, you create an integer array whose index range covers the entire range of values in your array to sort. Each time a value occurs in the original array, you increment the counter at that index. At the end, run through your counting array, printing the value of each non-zero valued index that number of times.

For example, consider an array arr = [1, 1, 3, 2, 1]. All of the values are in the range [0 . . . 3], so create an array of zeroes, result = [0, 0, 0, 0]. The results of each iteration follow:

Now we can print the sorted array: sorted = [1, 1, 1, 2, 3].

Challenge

Given an unsorted list of integers, use the counting sort method to sort the list and then print the sorted list.

Hint: You can use your previous code that counted the items to print out the actual values in order.

Function Description

Complete the countingSort function in the editor below. It should return the original array, sorted ascending, as an array of integers.

countingSort has the following parameter(s):

• arr: an array of integers

Input Format

The first line contains an integer n, the length of arr. The next line contains space-separated integers arr[i] where 0 <= i < n.

Constraints

• 0 <= n <= 1000000
• 0 <= arr[i] < 100

Output Format

Print the sorted list as a single line of space-separated integers.

Sample Input

100
63 25 73 1 98 73 56 84 86 57 16 83 8 25 81 56 9 53 98 67 99 12 83 89 80 91 39 86 76 85 74 39 25 90 59 10 94 32 44 3 89 30 27 79 46 96 27 32 18 21 92 69 81 40 40 34 68 78 24 87 42 69 23 41 78 22 6 90 99 89 50 30 20 1 43 3 70 95 33 46 44 9 69 48 33 60 65 16 82 67 61 32 21 79 75 75 13 87 70 33

Sample Output

1 1 3 3 6 8 9 9 10 12 13 16 16 18 20 21 21 22 23 24 25 25 25 27 27 30 30 32 32 32 33 33 33 34 39 39 40 40 41 42 43 44 44 46 46 48 50 53 56 56 57 59 60 61 63 65 67 67 68 69 69 69 70 70 73 73 74 75 75 76 78 78 79 79 80 81 81 82 83 83 84 85 86 86 87 87 89 89 89 90 90 91 92 94 95 96 98 98 99 99

Explanation

Once our counting array has been filled, loop from index 0 to the end, printing each i value arr[i] times.

Solution – Counting Sort 2 – HackerRank Solution

C++

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */
    int n , arri;
    cin >> n;
    vector<int> appears(100);
    for(int i=0; i<n ;i++){
        cin >> arri;
        appears[arri]++;
    }
    for(int i=0; i<100 ;i++){
        while(appears[i]>0){
            cout << i << " ";
            appears[i]--;
        }
    }
    cout << endl;
    return 0;
}

Python

import sys

def countingSort(arr):
    cnt = [0] * (max(arr) + 1)
    output = [0] * (len(arr))
    
    for el in arr:
        cnt[el] += 1
        
    total = 0
    for ind in range(len(cnt)):
        old = cnt[ind]
        cnt[ind] = total
        total += old
        
    for el in arr:
        output[cnt[el]] = el
        cnt[el] += 1
        
    return output

if __name__ == "__main__":
    n = int(input().strip())
    arr = list(map(int, input().strip().split(' ')))
    result = countingSort(arr)
    print (" ".join(map(str, result)))

Java

import java.io.*;
import java.util.*;

public class Solution {

    public static int[] count(int[] ar, int max){
        int[] counts = new int[max+1];
        for(Integer n : ar){
            counts[n] += 1;
        }
        return counts;
    }

    public static void printCount(int[] counts){
        for(int i = 0; i < counts.length; ++i){
            for(int j = 0; j < counts[i]; ++j){
                System.out.print(i + " ");
            }
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] ar = new int[n];
        for(int i=0;i<n;i++){
            ar[i]=in.nextInt();
        }
        int[] counts = count(ar, 99);
       // printArray(counts);
        printCount(counts);

    }

}

Note: This problem (Counting Sort 2) is generated by HackerRank but the solution is provided by CodingBroz. This tutorial is only for Educational and Learning purpose.