C

permutation and combination program in c

// C program to print all permutations with duplicates allowed 
#include <stdio.h> 
#include <string.h> 
  
/* Function to swap values at two pointers */
void swap(char *x, char *y) 
{ 
    char temp; 
    temp = *x; 
    *x = *y; 
    *y = temp; 
} 
  
/* Function to print permutations of string 
This function takes three parameters: 
1. String 
2. Starting index of the string 
3. Ending index of the string. */
void permute(char *a, int l, int r) 
{ 
int i; 
if (l == r) 
    printf("%s
", a); 
else
{ 
    for (i = l; i <= r; i++) 
    { 
        swap((a+l), (a+i)); 
        permute(a, l+1, r); 
        swap((a+l), (a+i)); //backtrack 
    } 
} 
} 
  
/* Driver program to test above functions */
int main() 
{ 
    char str[] = "ABC"; 
    int n = strlen(str); 
    permute(str, 0, n-1); 
    return 0; 
}