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/*
** PERMUTE.C - prints all permutations of an input string
**
** public domain demo by Jon Guthrie
*/
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
int charcmp(char *, char *);
void permute(char *, int, int);
int main(int argc, char *argv[])
{
int length;
if (2 > argc)
{
puts("Usage: PERMUTE string");
abort();
}
length = strlen(argv[1]);
/* It only works if they're printed in order */
qsort(argv[1], length, 1, (int(*)(const void *, const void *))charcmp);
permute(argv[1], 0, length);
return 0;
}
/*
** This function prints all of the permutations of string "array"
** (which has length "len") starting at "start."
*/
void permute(char *array, int start, int len)
{
int j;
char *s;
if(start < len)
{
if(NULL == (s = malloc(len)))
{
printf("\n\nMemory error!!!\a\a\n");
abort();
}
strcpy(s, array);
for(j=start ; j<len ; ++j)
{
int temp;
if((j == start) || (s[j] != s[start]))
{ /* For each character that's different */
/* Swap the next first character with... */
/* the current first */
temp = s[j];
s[j] = s[start];
s[start] = temp;
permute(s, start+1, len);
}
}
free(s);
}
else puts(array);
}
int charcmp(char *a, char *b)
{
return(*a - *b);
}
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