51-valid-braces.js

// Write a function that takes a string of braces, and determines if the order of
// the braces is valid.It should return true if the string is valid, and false if it's invalid.

// This Kata is similar to the Valid Parentheses Kata, but introduces new characters:
// brackets [], and curly braces {}. Thanks to @arnedag for the idea!
//
// All input strings will be nonempty, and will only consist of
// parentheses, brackets and curly braces: ()[]{}.
//
// What is considered Valid?
//
// A string of braces is considered valid if all braces are matched with the correct brace.
//
// Examples
//
// "(){}[]"   =>  True
// "([{}])"   =>  True
// "(}"       =>  False
// "[(])"     =>  False
// "[({})](]" =>  False

const validBraces = ([brace, ...rest], stack = []) => {
  const obj = { '(': ')', '[': ']', '{': '}' };
  if (!brace && !stack.length) { return true; }
  if (obj[brace]) { return validBraces(rest, [brace, ...stack]); }
  if (brace === obj[stack[0]]) { return validBraces(rest, stack.slice(1)); }
  return false;
};