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  1. #include <iostream>
  2. #include <array>
  3.  
  4. unsigned int fib_mod(unsigned int n, unsigned int m) {using M = std::array<unsigned int, 3>;
  5.     auto mul = [m] (M & me, const M & other) {
  6.         me[2] = ((me[1] * other[1]) % m + (me[2] * other[2]) % m) % m;
  7.         unsigned int me_1 = me[1];
  8.         me[1] = ((me[0] * other[1]) % m + (me[1] * other[2]) % m) % m;
  9.         me[0] = ((me[0] * other[0]) % m + (me_1 * other[1]) % m) % m;
  10.     };
  11.     M r{{1, 1, 0}}, e{{1, 0, 1}}, ans{e};
  12.     while (n) {
  13.         if (n & 1) {
  14.             mul(ans, r);
  15.         }
  16.         mul(r, M(r));
  17.         n /= 2;
  18.     }
  19.     return ans[1];
  20. }
  21.  
  22. int main() {
  23.     std::cout << fib_mod(1<<31, 1<<31) << std::endl;
  24.     return 0;
  25. }
Success #stdin #stdout 0s 3460KB
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2140540357
https://ideone.com/0TGSWI
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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