radix_sort.cpp

#include <bits/stdc++.h>
using namespace std;

void countSort(int arr[], int n, int exp)
{
    int output[n];
    int i, count[10] = {0};
    for (int i = 0; i < n; i++)
        count[(arr[i] / exp) % 10]++;
    for (int i = 1; i < 10; i++)
        count[i] += count[i - 1];
    for (int i = n - 1; i >= 0; i--)
    {
        output[count[(arr[i] / exp) % 10] - 1] = arr[i];
        count[(arr[i] / exp) % 10]--;
    }
    for (int i = 0; i < n; i++)
        arr[i] = output[i];
}

// The main function to that sorts arr[] of size n using
// Radix Sort
void RadixSort(int arr[], int n)
{
    // Find the maximum number to know number of digits
    int m = *max_element(arr, arr + n);
    // Do counting sort for every digit. Note that instead
    // of passing digit number, exp is passed. exp is 10^i
    // where i is current digit number
    for (int exp = 1; m / exp > 0; exp *= 10)
        countSort(arr, n, exp);
}

int main()
{
    int arr[] = {170, 45, 75, 90, 802, 24, 2, 66};
    int n = sizeof(arr) / sizeof(arr[0]);
    RadixSort(arr, n);
    cout << "Sorted array: \n";
    for (int i = 0; i < n; i++)
        cout << arr[i] << " ";
    return 0;
}