Added fibonacci.cpp

fibonacci.cpp

@@ -0,0 +1,53 @@
+#include <iostream>
+#include <cassert>
+#define ll long long 
+// The following code calls a naive algorithm for computing a Fibonacci number.
+//
+// What to do:
+// 1. Compile the following code and run it on an input "40" to check that it is slow.
+//    You may also want to submit it to the grader to ensure that it gets the "time limit exceeded" message.
+// 2. Implement the fibonacci_fast procedure.
+// 3. Remove the line that prints the result of the naive algorithm, comment the lines reading the input,
+//    uncomment the line with a call to test_solution, compile the program, and run it.
+//    This will ensure that your efficient algorithm returns the same as the naive one for small values of n.
+// 4. If test_solution() reveals a bug in your implementation, debug it, fix it, and repeat step 3.
+// 5. Remove the call to test_solution, uncomment the line with a call to fibonacci_fast (and the lines reading the input),
+//    and submit it to the grader.
+
+ll fibonacci_naive(ll n) {
+    if (n <= 1)
+        return n;
+
+    return fibonacci_naive(n - 1) + fibonacci_naive(n - 2);
+}
+
+ll fibonacci_fast(ll n) {
+    if (n <= 1)
+        return n;
+	ll first=0,second=1;
+    ll third;
+    for(ll i=2;i<=n;i++)
+    {
+    	third=first+second;
+    	first=second;
+    	second=third;
+   	}
+    return third;
+}
+
+void test_solution() {
+    assert(fibonacci_fast(3) == 2);
+    assert(fibonacci_fast(10) == 55);
+    for (int n = 0; n < 20; ++n)
+        assert(fibonacci_fast(n) == fibonacci_naive(n));
+}
+
+int main() {
+    ll n = 0;
+    std::cin >> n;
+
+    //std::cout << fibonacci_naive(n) << '\n';
+    //test_solution();
+    std::cout << fibonacci_fast(n) << '\n';
+    return 0;
+}