js: fibonacci

// O(2^N)
const fibonacci = function(n){
    return n < 2 ? n : fibonacci(n-1) + fibonacci(n-2);
}


// to speed it up - O(2N)
function fibMemo(num, memo = {}) {
  if (memo[num]) return memo[num];
  if (num <= 1) return 1;

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


// fastest - O(N)
function fibWhile(num){
  var a = 1, b = 0, temp;

  while (num >= 0){
    temp = a;
    a = a + b;
    b = temp;
    num--;
  }

  return b;
}