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  1. #include <iostream>
  2. #include <cmath>
  3.  
  4. unsigned largest_prime_factor(unsigned n)
  5. {
  6.     unsigned lpf = 0;
  7.     unsigned stop = sqrt(n);
  8.     for (unsigned i=2; i<=stop; ++i)
  9.         if (n%i==0) {
  10.             lpf = i;
  11.             while (n%i==0) { n/= i; }
  12.             stop = sqrt(n);
  13.         }
  14.     return n==1 ? lpf : n;
  15. }
  16.  
  17. int main()
  18. {
  19.     std::cout << largest_prime_factor(2147483647) << "\n";
  20.     std::cout << largest_prime_factor(4294967291) << "\n";
  21.     std::cout << largest_prime_factor(4294967294) << "\n";
  22.     std::cout << largest_prime_factor(65536) << "\n";
  23.     std::cout << largest_prime_factor(2*2*2*7*13*19) << "\n";
  24. }
Success #stdin #stdout 0s 2852KB
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stdin
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Standard input is empty
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2147483647
4294967291
2147483647
2
19
https://ideone.com/fuBcC6
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
secret

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