C Program to Permute All Letters of an Input String

This is a C program to permute all the letters of an input string.

This algorithm finds all permutations of the letters of a given string. It is a recursive algorithm using concept of backtracking.

Here is the source code of the C program to permute all letters of an input string. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
#include <stdio.h>
```
```
#include <string.h>
```
```
void swap (char *x, char *y)
```
```
{
```
```
    char temp;
```
```
    temp = *x;
```
```
    *x = *y;
```
```
    *y = temp;
```
```
}
```
```
 
```
```
void permute(char *a, int i, int n) 
```
```
{
```
```
   int j; 
```
```
   if (i == n)
```
```
     printf("%s\n", a);
```
```
   else
```
```
   {
```
```
        for (j = i; j <= n; j++)
```
```
       {
```
```
          swap((a + i), (a + j));
```
```
          permute(a, i + 1, n);
```

          swap((a + i), (a + j)); //backtrack

```
       }
```
```
   }
```
```
} 
```
```
 
```
```
int main()
```
```
{
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```
   char str[21];
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   int len;
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```
   printf("\nEnter a string: ");
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```
   scanf("%s", str);
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   len = strlen(str);
```
```
   permute(str, 0, len - 1);
```
```
   return 0;
```
```
}
```

$ gcc permute.c -o permute
$ ./permute
 
Enter a string: SAN
 
All possible permutations are:
    SAN
    SNA
    ASN
    ANS
    NAS
    NSA

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