bool next_digit_permutation(uint32_t &number) {
if(!number) return false; // no elements
if(number < 10) return false; // single element
uint32_t pivot = number % 10;
uint32_t front = number / 10;
uint32_t order = 10;
while(pivot <= front%10) {
pivot = front%10;
front /= 10;
order *= 10;
if(!front) { // last permutation already
number = reverse_digits(number);
return false;
}
}
pivot = front%10;
uint32_t mid = number - front*order;
uint32_t mfront = mid;
uint32_t morder = 1;
while(mfront%10 <= pivot) {
mfront /= 10;
morder *= 10;
}
front = front - pivot + mfront%10;
uint32_t back = mid - mfront*morder;
mfront = (mfront - mfront%10 + pivot)*morder + back;
number = front*order + reverse_digits(mfront);
return true;
}
constexpr bool is_parindrome(int cand)
{
return cand == reverse_digits(cand, 0);
}
constexpr int reverse_digits(int in, int out)
{
return (in == 0) ? out : reverse_digits(in / 10, out * 10 + in % 10);
}
