Write a C program to print all permutations of a given string

A permutation, also called an “arrangement number” or “order,” is a rearrangement of the elements of an ordered list S into a one-to-one correspondence with S itself. A string of length n has n! permutation.



Below are the permutations of string ABC.
ABC, ACB, BAC, BCA, CAB, CBA
Here is a solution using backtracking.

// 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\n", 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; }

Output:

ABC
ACB
BAC
BCA
CBA
CAB

Algorithm Paradigm: Backtracking
Time Complexity: O(n*n!)