C Program to find all permutations of string

Write a C Program to find all the permutations of string using Recursion and Iteration. Here’s simple Program to print all permutations of string using Recursion and Iteration in C Programming Language.

Recursion : :

Recursion is the process of repeating items in a self-similar way. In programming languages, if a program allows you to call a function inside the same function, then it is called a recursive call of the function.

The C programming language supports recursion, i.e., a function to call itself. But while using recursion, programmers need to be careful to define an exit condition from the function, otherwise it will go into an infinite loop.

Recursive functions are very useful to solve many mathematical problems, such as calculating the factorial of a number, generating Fibonacci series, etc.

Iteration : :

Iteration, in the context of computer programming, is a process wherein a set of instructions or structures are repeated in a sequence a specified number of times or until a condition is met.

When the first set of instructions is executed again, it is called an iteration. When a sequence of instructions is executed in a repeated manner, it is called a loop.

Example : :

for (int i=0;i<n;i++)
{
\\ statements;
}

Below is the source code for C Program to find all permutations of string by Recursion and Iteration which is successfully compiled and run on Windows System to produce desired output as shown below :

SOURCE CODE : :

/* C Program to find all permutations of string by Recursion and Iteration */


#include<stdio.h>
#include<string.h>

void Permute1(char str[], char* currentptr);
void Permute2(char str[], int startIndex, int lastIndex);
void Swap(char *a, char *b);

int main()
{
        char str[20];
        printf("Enter any String :: ");
        scanf("%s",str);
        printf("\nUsing Iteration :: \n\n");
        Permute1(str,str);
        printf("\n\n");
        printf("\nUsing Recursion :: \n\n");
        Permute2(str,0,strlen(str)-1);

        printf("\n");

        return 0;
}

//--------------Iteration---------------------

void Permute1(char str[], char* currentptr)
{
        char *ptr;
        if( *(currentptr + 1) == '\0')
           printf("%s\t", str);
        else
        for(ptr=currentptr; *ptr!='\0'; ptr++)
    {
                Swap(ptr,currentptr);
                Permute1(str, currentptr+1);
                Swap(ptr,currentptr);
        }
}

//--------------Recursion---------------------

void Permute2(char str[], int startIndex, int lastIndex)
{
        int i;
        if(startIndex==lastIndex)
        {
                for(i=0;i<=lastIndex;i++)
                        printf("%c",str[i]);
                printf("\t");
        }
        else
        for(i=startIndex;i<=lastIndex;i++)
        {
                Swap(&str[startIndex], &str[i]);
                Permute2(str,startIndex+1,lastIndex);
                Swap(&str[startIndex], &str[i]);
        }
}


void Swap(char *a, char *b)
{
        char temp = *a;  *a=*b; *b=temp;
}

OUTPUT : :

****************** OUTPUT *********************


****************** FIRST RUN ******************

Enter any String :: xyz

Using Iteration ::

xyz     xzy     yxz     yzx     zyx     zxy


Using Recursion ::

xyz     xzy     yxz     yzx     zyx     zxy



****************** SECOND RUN ******************

Enter any String :: abcd

Using Iteration ::

abcd    abdc    acbd    acdb    adcb    adbc    bacd    badc    bcad    bcda 
bdca    bdac    cbad    cbda    cabd    cadb    cdab    cdba    dbca    dbac 
dcba    dcab    dacb    dabc


Using Recursion ::

abcd    abdc    acbd    acdb    adcb    adbc    bacd    badc    bcad    bcda 
bdca    bdac    cbad    cbda    cabd    cadb    cdab    cdba    dbca    dbac 
dcba    dcab    dacb    dabc

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