Tail Recursion Fibonacci

Question

How do I implement a recursive Fibonacci function with no loops running in O(n)?

Answer 1

Scala code for finding nth Fibonacci Number. For more information on Tail Recursion http://nerds.logdown.com/posts/1406258-n-th-fibonacci-number

object Main {
     def main(args: Array[String]) {
        println(fib(9));
        println(fib(8));
        println(fib(7));
        println(fib(6));
        println(fib(5));
        println(fib(4));
        println(fib(3));
        println(fib(2));
        println(fib(1));
        println(fib(0));
      }
      def fib(n: Int): Int = {
        def fib(n: Int, p :Int, c: Int): Int ={
          if (n == 0) return -1; // undefined
          if (n == 1) return p;
          fib(n-1, c, p + c)
        }
        fib(n, 0, 1);
      }
    }