// Program to print all combination of size r in an array of size n
#include <stdio.h>
#include <stdlib.h>
void combinationUtil(int arr[], int data[], int start, int end, int index, int r);

// Needed for qsort.  See http://w...content-available-to-author-only...s.com/reference/cstdlib/qsort/
int compare (const void * a, const void * b)
{  return ( *(int*)a - *(int*)b );  }

// The main function that prints all combinations of size r
// in arr[] of size n. This function mainly uses combinationUtil()
void printCombination(int arr[], int n, int r)
{
    // A temporary array to store all combination one by one
    int data[r];

    // Sort array to handle duplicates
    qsort (arr, n, sizeof(int), compare);

    // Print all combination using temprary array 'data[]'
    combinationUtil(arr, data, 0, n-1, 0, r);
}

/* arr[]  ---> Input Array
   data[] ---> Temporary array to store current combination
   start & end ---> Staring and Ending indexes in arr[]
   index  ---> Current index in data[]
   r ---> Size of a combination to be printed */
void combinationUtil(int arr[], int data[], int start, int end, int index, int r)
{
    // Current combination is ready to be printed, print it
    if (index == r)
    {
        for (int i=0; i<r; i++)
            printf("%d " ,data[i]);
        printf("\n");
        return;
    }

    // replace index with all possible elements. The condition
    // "end-i+1 >= r-index" makes sure that including one element
    // at index will make a combination with remaining elements
    // at remaining positions
    for (int i=start; i<=end && end-i+1 >= r-index; i++)
    {
        data[index] = arr[i];
        combinationUtil(arr, data, i+1, end, index+1, r);


        // Remove duplicates
        while (arr[i] == arr[i+1])
             i++;
    }
}

// Driver program to test above functions
int main()
{
    int arr[] = {1, 2, 1, 3, 1};
    int r = 3;
    int n = sizeof(arr)/sizeof(arr[0]);
    printCombination(arr, n, r);
}