README.md

Challenge #4: 😵‍💫 Turn the parentheses around

In Santa's workshop 🎅, some Christmas messages have been written in a peculiar way: the letters inside the parentheses must be read in reverse.

Santa needs these messages to be correctly formatted. Your task is to write a function that takes a string of text and reverses the characters within each pair of parentheses, removing the parentheses in the final message.

However, keep in mind that nested parentheses may exist, so you must reverse the characters in the correct order.

const a = decode("hola (odnum)");
console.log(a); // hola mundo

const b = decode("(olleh) (dlrow)!");
console.log(b); // hello world!

const c = decode("sa(u(cla)atn)s");
console.log(c); // santaclaus

// Step by step:
// 1. We reverse the nesting -> sa(ualcatn)s
// 2. We reverse what remains -> santaclaus

Warning

To take into account:

• The input strings will always be well-formed with properly matching parentheses; you don't need to validate them.

• There should be no parentheses left in the final message.

• The maximum level of nesting is 2.

Solution

Important

This regex is designed to find and capture text enclosed within parentheses. The captured content is everything between the opening "(" and closing ")" parentheses. The g flag ensures that all matches in the input string are found, not just the first one.

/\(  (  [^()]+  )  \)/g
     ^          ^

• The first match captures the text within the outermost parentheses.
• The second match captures the text within the innermost parentheses, taking into account nested structures.

JavaScript

280 points

function decode(message) {
  const regex = /\(([^()]+)\)/g;
  const replacer = (_, group) => [...group].reverse().join("");

  return message.replace(regex, replacer).replace(regex, replacer);
}

TypeScript

280 points

function decode(message: string): string {
  const regex = /\(([^()]+)\)/g;
  const replacer = (_, group) => [...group].reverse().join("");

  return message.replace(regex, replacer).replace(regex, replacer);
}