int32 problem104() {
BigInteger f1(1);
BigInteger f2(1);
int32 k = 2;
string front = "123456789";
string back = "123456789";
while (true) {
k++;
BigInteger temp = f1 + f2;
f1 = f2;
f2 = temp;
if (temp.numberOfDigits() < 18) {
continue;
}
for (int32 i = 0; i < 9; i++) {
back[i] = temp.getNthDigitFromRight(i) + '0';
}
if (isPandigital(back)) {
for (int32 i = 0; i < 9; i++) {
front[i] = temp.getNthDigitFromLeft(i) + '0';
}
if (isPandigital(front)) {
return k;
}
}
}
}
BigInteger multiply(BigInteger &x, int y, int pos = 0) {
int nx = x.numberOfDigits();
BigInteger z;
int carry = 0;
for (int i = 0; i < nx; i++) {
carry += x.getDigit(i) * y;
z.setDigit(pos++, carry % 10);
carry /= 10;
}
while (carry > 0) {
z.setDigit(pos++, carry % 10);
carry /= 10;
}
return z;
}
