/* A Brilliant number is a semiprime that can be obtained only by multiplicating two, and only two, different primes with the same number of digits. A semiprime can be: A composite number equal to the product of two different primes.A composite number equal to the square of a prime. Given an integer n, implement a function that returns true if n is a Brilliant number, or false if it's not. isBrilliant(11) ➞ false // 11 is a prime. isBrilliant(9) ➞ true // 9 is equal to the square of a prime: 3² isBrilliant(21) ➞ true // 21 is equal to the product of two different primes: 3 x 7 // 3 and 7 have the same digital length. isBrilliant(22) ➞ false // 22 is equal to the product of two different primes: 2 x 11 // 2 and 11 have different digital lengths. Note: Press submit for default value of 25 */ #include #include #include using namespace std; using ull = unsigned long long; // standard prime check auto is_prime = [](ull num){ if (num < 2) return false; if (num == 2) return true; if (!(num & 1)) return false; for(ull i=3, lim=sqrt(num)+1; i<=lim; i+=2) if (!(num%i)) return false; return true; }; // get length of digit using log10 auto len = [](ull num) { return floor(log10(num))+1; }; auto check_bright = [](ull num) { auto bri_hlpr = [=](ull div1, ull div2){ if(is_prime(div1) && is_prime(div2) && len(div1) == len(div2)) return true; return false; }; // check for 2 explicitly if(bri_hlpr(2, num/2)) return true; // check only odd divisors since primes // other than 2 are odd for(ull i=3,lim=num/2; i<=lim; i+=2) if(!(num%i)) if(bri_hlpr(i, num/i)) return true; return false; }; int main() { ull num{25}; cin >> num; for(auto n : vector{num,2,4,6,9,8,18,10,14,15,20,21,30,49,50, 101,451,786,10403,12707,44069,44070, 240199, 240201,664189,66420}){ cout << n << boolalpha << " is Bright Number ? "; if(is_prime(n)) cout << "false\n"; else cout << check_bright(n) << '\n'; } }

[Challenge] Bright Number.cpp