fibonacci number fast algorithm

Programs- Coder/C++/Fibonacci series/fibonacci_optimised.cpp

@@ -0,0 +1,27 @@
+#include <iostream>
+using namespace std;
+int fibonacci_naive(int n) {
+    if (n <= 1)
+        return n;
+
+    return fibonacci_naive(n - 1) + fibonacci_naive(n - 2);
+}
+
+int fibonacci_fast(int n) {
+    int prev = 0, next = 1, ans;
+    if(n==0) return prev;
+    for(int i=2; i<=n ; i++){
+        ans = prev + next;
+        prev = next;
+        next = ans;
+    }
+
+    return next;
+}
+
+int main() {
+    int n = 0;
+    cin >> n;
+    cout << fibonacci_fast(n) << '\n';
+    return 0;
+}