// An efficient way to calculate nth fibonacci number faster and simpler than // O(nlogn) method of matrix exponentiation This works by using both recursion // and dynamic programming. as 93rd fibonacci exceeds 19 digits, which cannot be // stored in a single long long variable, we can only use it till 92nd fibonacci // we can use it for 10000th fibonacci etc, if we implement bigintegers. // This algorithm works with the fact that nth fibonacci can easily found if we // have already found n/2th or (n+1)/2th fibonacci It is a property of fibonacci // similar to matrix exponentiation. #include #include using namespace std; const long long MAX = 93; long long f[MAX] = {0}; long long fib(long long n) { if (n == 0) return 0; if (n == 1 || n == 2) return (f[n] = 1); if (f[n]) return f[n]; long long k = (n % 2 != 0) ? (n + 1) / 2 : n / 2; f[n] = (n % 2 != 0) ? (fib(k) * fib(k) + fib(k - 1) * fib(k - 1)) : (2 * fib(k - 1) + fib(k)) * fib(k); return f[n]; } int main() { // Main Function for (long long i = 1; i < 93; i++) { cout << i << " th fibonacci number is " << fib(i) << "\n"; } return 0; }