Here's your ...:

use Inline C => <<EOT;
UV score(char* a, char* b) {  /* it doesn't like const... */
  char mark[256] = { 0 }, * i;
  UV sc = 0;
  for(i = a; *i; mark[*i++] = 1);
  for(i = b; *i; i++)
    if(mark[*i])
      sc += mark[*i]--;
  return sc;
}
EOT
[download]

Yep, you're right, it won't work for Unicode. Modification to do so is left as an excercise for the diligent student.

czth