permutations_with_no_duplicates_v1.c

/*

    permutations_with_no_duplicates_v1.c

    https://www.codesdope.com/blog/article/generating-permutations-of-all-elements-of-an-arra/


    You can find all my C programs at Dragan Milicev's pastebin:

    https://pastebin.com/u/dmilicev

*/

#include <stdio.h>

//function to print the array of n integers
void print_array(int arr[], int n)
{
    int i,j;

    printf("\n");

    for(i=0; i<n; i++)
        printf("%2d", arr[i]);

    printf("\n");
}

// function to swap the variables a and b
void swap(int *a, int *b)
{
    int temp;
    temp = *a;
    *a = *b;
    *b = temp;
}

// recursive function to generate permutation
void permutation(int *arr, int start, int end)
{
    int i;

    if(start==end)
    {
        print_array(arr, end+1);        // this is one permutation
        return;
    }

    for( i=start; i<=end; i++ )         // fixing one first digit,
    {
        swap((arr+i), (arr+start));     // swapping numbers
        permutation(arr, start+1, end); // and calling permutation on the rest of the digits
        swap((arr+i), (arr+start));     // swapping numbers
    }
} // permutation()


int main(void)
{
    int i, n;

    printf("Enter the size of array n = ");
    scanf("%d",&n);

    int arr[n];                 // array of n permutation elements

    for (i = 0; i < n; i++)     // fill in the array with integers from 1 to n
        arr[i] = i + 1;

    permutation(arr, 0, n-1);   //calling recursive function to generate permutations

    return 0;
} // main()