50 lines
1.2 KiB
C++
50 lines
1.2 KiB
C++
#include <cstdio>
|
|
|
|
#define MIN(a, b) (((a) < (b)) ? (a) : (b))
|
|
|
|
/**
|
|
* 479. Largest Palindrome Product
|
|
* Given an integer n, return the largest palindromic integer that can be represented as the product of two n-digits integers. Since the answer can be very large, return it modulo 1337.
|
|
*/
|
|
|
|
class Solution {
|
|
private:
|
|
static inline constexpr unsigned long long get9(int n) {
|
|
unsigned long long ans = 0;
|
|
while (n--)
|
|
ans = ans * 10 + 9;
|
|
return ans;
|
|
}
|
|
|
|
static inline constexpr int getAns(int n) {
|
|
auto halfMax = get9(n), halfMin = 1 + get9(n - 1);
|
|
for (auto i = halfMax; i >= halfMin; --i) {
|
|
unsigned long long iFull = 0;
|
|
for (auto j = i; j; j /= 10) {
|
|
iFull = 10 * iFull + j % 10;
|
|
}
|
|
iFull += i * (1 + halfMax);
|
|
for (auto j = MIN(halfMax, iFull / halfMin); iFull / j <= halfMax && j >= halfMin; --j) {
|
|
if (iFull % j == 0) {
|
|
// std::printf("%llu %llu\n", iFull, j);
|
|
return iFull % 1337;
|
|
}
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
public:
|
|
static constexpr int largestPalindrome(int n) {
|
|
// const static int ans[] = {-1, 9, 987, 123, 597, 677, 1218, 877, 475};
|
|
// return ans[n];
|
|
return n == 1 ? 9 : getAns(n);
|
|
}
|
|
};
|
|
|
|
int main() {
|
|
for (int i = 2; i <= 8; ++i) {
|
|
// std::printf("%d\n", getAns(i));
|
|
}
|
|
return 0;
|
|
}
|