Chapter 9, Designing Functions – Recursion

9.1 Into reverse: An empty string is reversed by simply doing nothing. To reverse a non-empty string, remove its first character, reverse the rest, and append the removed character at the end. For example, reverse("MONTEVIDEO") can be found by doing reverse("ONTEVIDEO")+"M". In the same way, reverse("ONTEVIDEO") would be equal to reverse("NTEVIDEO")+"O", and so on:

const reverse = (str: string): string =>
  str.length === 0 ? "" : reverse(str.slice(1)) + str[0];

9.2 Climbing steps: To climb a ladder with n steps, we can act in two ways:

• Climb one single step and then climb an (n-1) steps ladder
• Climb two steps at once and then climb an (n-2) steps ladder

So, if we call ladder(n) the number of ways to climb a steps ladder, we know that ladder(n)= ladder(n-1) + ladder(n-2). Adding the fact that ladder(0)=1 (there’s only one...