/* Given a set of consecutive characters, find a hash expression that
   would produce the desired symbols.

   Result:
   ('A' * 105 ^ 99) * 3 % 53 = '\n'
   ('B' * 105 ^ 99) * 3 % 53 = '"'
   ('C' * 105 ^ 99) * 3 % 53 = ' '
   ('D' * 105 ^ 99) * 3 % 53 = '/'
*/

#include<stdio.h>

/* Hash function. */
static int Hash(char input, int p, int q, int r, int s)
{
   return (input * p ^ q) * r % s;
}

static void TryKeySet(const char *keys)
{
   int p, q, r, s, v, coverage;
   const char *k;

   for(p = 1; p < 1000; p++)
   {
      for(q = 1; q < 1000; q++)
      {
         for(r = 1; r < 1000; r++)
         {
            for(s = 48; s < 1000; s++)
            {
               if( Hash(keys[0], p, q, r, s) != '\n' ) continue;
               if( Hash(keys[1], p, q, r, s) != '"' ) continue;

               coverage = 0;
               v = Hash(keys[2], p, q, r, s);
               coverage |= v == ' ' ? 1 : (v == '/' ? 2 : 0);
               v = Hash(keys[3], p, q, r, s);
               coverage |= v == ' ' ? 1 : (v == '/' ? 2 : 0);

               if( coverage == 3 )
               {
                  printf("keys = %s, p = %d, q = %d, r = %d, s = %d:",
                         keys, p, q, r, s);
                  for(k = keys; *k; k++)
                     printf("\t%d->%d", *k, Hash(*k, p, q, r, s));
                  putchar('\n');
               }
            }
         }
      }
   }
}

int main(void)
{
   TryKeySet("ABCD");
   return 0;
}