Thread: string permutation problem

I'm trying to write a simple string permutation program. The program takes a string and displays all permutations of the string. However, the code needs a little debug, and I'm out of patience. I've worked on this faaar too long. Can anyone find the problem.

The function that does the work is called perm().
Here's perm():

Code:

void perm(char* str, int n, int len){
  int i,k,j;
  char* tmp, ch; 

  tmp = malloc((len+1) * sizeof(char));
  if(!tmp){
    puts("\ncall to malloc() failed.");
    exit(1);
  }

  strcpy(tmp, str);

  for(i=0; i<len; i++){

    //rotate string i times, so next letter is first in line.
    for(j=0; j<i; j++){
      ch = tmp[0];
      for(k=0; k<len-1; k++) tmp[k] = tmp[k+1];
      tmp[len-1] = ch;
      tmp[len] = '\0';
    }
    A[n] = tmp[0];
    for(j=0; j<len; j++) tmp[j] = tmp[j+1];
    if(n<len) perm(tmp, n+1, len-1);
    else{
      A[n+1] = tmp[0];
      printf("\npermy: %s", A);
    }
  }
}

A[] is global and contains each permutation of str. perm() is called the first time like this:

Code:

perm(str, 0, len);

where str is a pointer to a string of length len.

The problem is the same as always, I've overstepped an array somewhere. I've run out of patience. Can you find the problem?

Compare your algorithm with this.