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Print all permutations of a string and share the complexity of the algorithm?

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Print all permutations of a string and share the complexity of the algorithm?
posted Oct 14, 2015 by anonymous

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1 Answer

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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

enter image description here

// 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!)

answer Oct 15, 2015 by Mohammed Hussain
will you help me to understand backtracking over here and why we are using it?
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