Fibonacci sequence

example 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...

Formula F(n) = F(n-1) + F(n-2)

Recursive

function fibonacci(num) {
  if (num <= 1) return 1;

  return fibonacci(num - 1) + fibonacci(num - 2);
}

Recursive with memorization

function fibonacci(num, memo) {
  memo = memo || {};

  if (memo[num]) return memo[num];
  if (num <= 1) return 1;

  return memo[num] = fibonacci(num - 1, memo) + fibonacci(num - 2, memo);
}