fibonacci iterative and recursive

// Given a number N return the index value of the Fibonacci sequence, where the sequence is:

// 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144 ...
// the pattern of the sequence is that each value is the sum of the 2 previous values, that means that for N=5 → 2+3

//For example: fibonacciRecursive(6) should return 8

// O(n)
function fibonacciIterative(n: number) {
  let fib = [0, 1];
  for (let i = 2; i <= n; i++) {
    fib[i] = fib[i - 1] + fib[i - 2];
  }

  return fib[n];
}

// O(2 ^ n)
function fibonacciRecursive(n: number): number {
  if (n < 2) {
    return n;
  };

  return fibonacciRecursive(n - 2) + fibonacciRecursive(n - 1);
}

let val = 6;
console.log('Fibonacci recursive ' + val + ': ' + fibonacciRecursive(val));
console.log('Fibonacci iterative ' + val + ': ' + fibonacciIterative(val));
val = 10;
console.log('Fibonacci recursive ' + val + ': ' + fibonacciRecursive(val));
console.log('Fibonacci iterative ' + val + ': ' + fibonacciIterative(val));