hasBalancedParen

hasBalancedParen.js

// Parentheses Tally
const newOpenCnt = (c, openCnt) => {
  if (c === '(') return openCnt + 1
  if (c === ')') return openCnt - 1
  return openCnt
}

function isBalanced(str, openCnt) {
  // Continue or Stop?
  if (typeof str !== 'string') return false
  if (openCnt <  0) return false
  if (str.length === 0) return openCnt === 0

  // What to Look At Next?
  const fst = str[0]
  const rst = str.slice(1)
  return isBalanced(rst, newOpenCnt(fst, openCnt))
}

function hasBalancedParen(str) {
  return isBalanced(str, 0)
}