C Exercises: Counting sort algorithm

C Programming Searching and Sorting Algorithm: Exercise-8 with Solution

Write a C program for counting sort.

Note:
According to Wikipedia "In computer science, counting sort is an algorithm for sorting a collection of objects according to keys that are small integers; that is, it is an integer sorting algorithm. It operates by counting the number of objects that have each distinct key value, and using arithmetic on those counts to determine the positions of each key value in the output sequence. Its running time is linear in the number of items and the difference between the maximum and minimum key values, so it is only suitable for direct use in situations where the variation in keys is not significantly greater than the number of items. However, it is often used as a subroutine in another sorting algorithm, radix sort, that can handle larger keys more efficiently".

Sample Solution:

Sample C Code:

#include <stdio.h>
/* Counting sort function */
int counting_sort(int a[], int k, int n) {
    int i, j;
    int b[15], c[100];
    // Initialize the count array
    for (i = 0; i <= k; i++)
        c[i] = 0;
    // Count the occurrences of each element in the input array
    for (j = 1; j <= n; j++)
        c[a[j]] = c[a[j]] + 1;
    // Update the count array to contain the cumulative count of elements
    for (i = 1; i <= k; i++)
        c[i] = c[i] + c[i - 1];
    // Build the sorted array based on the count array
    for (j = n; j >= 1; j--) {
        b[c[a[j]]] = a[j];
        c[a[j]] = c[a[j]] - 1;
    }
    // Display the sorted array
    printf("The Sorted array is: ");
    for (i = 1; i <= n; i++)
        printf("%d,", b[i]);
}
int main() {
    int n, k = 0, a[15], i;
    // Input the number of elements
    printf("Input number of elements: ");
    scanf("%d", &n);
    // Input the array elements one by one
    printf("Input the array elements one by one: \n");
    for (i = 1; i <= n; i++) {
        scanf("%d", &a[i]);
        // Update the maximum element value
        if (a[i] > k) {
            k = a[i];
        }
    }
    // Call the counting_sort function to sort the array
    counting_sort(a, k, n);
    printf("\n");
    return 0;
}

Sample Input:

3
12
15
56

Sample Output:

Input number of elements:  Input the array elements one  by one: 
The Sorted array is : 12,15,56,

Flowchart:

C Programming Code Editor:

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