Digitos_Diferentes - C

/*
  INPUT:
    87 104
    989 1022
    22 25
    1234 1234
  OUTPUT:
    14
    0
    3
    1
*/

#include <stdio.h>

#define f(i, s, t) for (int i = s; i < t; ++i)

int main() {
  int n, m, a, b, c, d, ans;
  while(scanf("%d%d", &n, &m) != EOF) {
    ans = 0;
    f(i,n,m+1) {
      a = i / 1000, b = i % 1000 / 100,
      c = i % 100 / 10, d = i % 10;
      if(!a) a = -1;
      if(!b && a == -1) b = -1;
      if(!c && b == -1) c = -1;
      if((a == -1 || (a != b && a != c && a != d)) && (b == -1 || (b != c && b != d)) && (c == -1 || (c != d))) {
        ++ans;
      }
    }
    printf("%d\n", ans);
  }
}