13.js

/**
 * @param {string} s
 * @return {number}
 */
var romanToInt = function (str) {
  let sum = 0
  for (let i = 0; i < str.length; i++) {
    if (i + 1 < str.length && Symbol[str[i] + str[i + 1]]) {
      sum += Symbol[str[i] + str[i + 1]]
      i++
    } else {
      sum += Symbol[str[i]]
    }
  }
  return sum
}

const Symbol = {
  I: 1,
  V: 5,
  X: 10,
  L: 50,
  C: 100,
  D: 500,
  M: 1000,
  IV: 4,
  IX: 9,
  XL: 40,
  XC: 90,
  CD: 400,
  CM: 900,
}