20. 有效的括号

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function (s) {
  let arr = s.split('')
  let stack = []
  let map = new Map([
    ['(', ')'],
    ['[', ']'],
    ['{', '}'],
  ])
  if (arr.length % 2 !== 0) {
    return false
  }
  for (let i = 0; i < arr.length; i++) {
    if (map.has(arr[i])) {
      stack.push(arr[i])
    } else {
      if (map.get(stack.pop()) !== arr[i]) {
        return false
      }
    }
  }
  return !stack.length
}