Lame JS puzzle #4

fb.js

/*
  Translate roman numbers to decimals. If a roman letter/number is lesser than the next one substract, otherwise add.
*/

// Time-Complexity = O(n)
// Space-Complexity = O(1)

const Romans = {
  I: 1,
  V: 5,
  X: 10,
  L: 50
}

// LXIV -> 64

function romanToDec(roman) {
  if (!roman.length)
    return 0;

  let dec = 0;
  let prevRoman = roman[0];
  
  // Skip first letter
  for (let i = 1; i < roman.length; i++) {
    // Test:
    // 1. roman[i] == X, prevRoman == L, dec == 50
    // 2. roman[i] == I, prevRoman == X, dec == 60
    // 3. roman[i] == V, prevRoman == I, dec == 59  
    if (Romans[prevRoman] < Romans[roman[i]])
      dec -= Romans[prevRoman];
    else
      dec += Romans[prevRoman];
    
    prevRoman = roman[i];
  }
  
  // 4. prevRoman == V, dec == 64
  dec += Romans[prevRoman];
  
  return dec;
}

console.log(romanToDec("LXIV"));

fb_recursive.js

/*
  Translate roman numbers to decimals. If a roman letter/number is lesser than the next one substract, otherwise add.
*/

// Time-Complexity = O(n)
// Space-Complexity = O(1)

const Romans = {
  I: 1,
  V: 5,
  X: 10,
  L: 50
}

// LXIV -> 64

function _romanToDec(roman, i, acc) {
  let prevRoman = Romans[roman[i - 1]];

  if (i == roman.length)
    return acc + prevRoman;
  
  if (prevRoman < Romans[roman[i]])
    acc -= prevRoman;
  else
    acc += prevRoman;
  
  return _romanToDec(roman, i + 1, acc);
}

function romanToDec(roman) {
  return _romanToDec(roman, 1, 0);
}

console.log(romanToDec("LXIV"));