Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

Input: s = "III";
Output: 3;

Input: s = "IX";
Output: 9;

Input: s = "LVIII";
Output: 58;
Explanation: (L = 50), (V = 5), (III = 3);

Input: s = "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

function romanToInt(s) {
  const key = {
    I: 1,
    V: 5,
    X: 10,
    L: 50,
    C: 100,
    D: 500,
    M: 1000
  };

  let result = [];

  for (let i = 0; i < s.length; i++) {
    if (key[s[i]] < key[s[i + 1]]) {
      result.push(key[s[i + 1]] - key[s[i]]);
      i++;
      continue;
    } else {
      result.push(key[s[i]]);
    }
  }

  return result.reduce((prev, current) => prev + current);
}

function romanToInt(s) {
  const key = {
    I: 1,
    V: 5,
    X: 10,
    L: 50,
    C: 100,
    D: 500,
    M: 1000
  };

  let result = 0;

  for (let i = 0; i < s.length; i++) {
    const cur = key[s[i]];
    const next = key[s[i + 1]];

    if (cur < next) {
      result += next - cur;
      i++;
    } else {
      result += cur;
    }
  }

  return result;
}