xint pandigit_mul_concat(xint n)
{
xint i=1;
xint p=0;
while ( !pandigital1to9_p(p) && digits_in(p)<10 ) {
xint next = n * i;
if ( p>0 ) p *= power(10, digits_in(next));
p += next;
++i;
}
return p;
}
int main()
{
xint max = 0;
for ( xint n=1; ; ++n ) {
xint p = pandigit_mul_concat(n);
if ( !pandigital1to9_p(p) || digits_in(p) > 9 )
continue;
if ( digits_in(n) > 4 )
break;
if ( p > max ) {
max = p;
printf("-- %s for n=%s\n", str(max), str(n));
}
}
printf("end\n");
}
int digits_in(int num)
{
if (num == 0) {
return 1; // log10() chokes on 0
}
if (num < 0) {
return 1 + digits_in(0 - num); // 1 extra for the - character
}
return 1 + log10(num); // 1 extra since log10 is logarythmic
}