romanToInt.js

/**
 * @param {string} s
 * @return {number}
 */
var romanToInt = function(s) {
  // make a map of chars
  var romanNumMap = {
    'I': 1,
    'V': 5,
    'X': 10,
    'L': 50,
    'C': 100,
    'D': 500,
    'M': 1000
  };
  
  var checkpoints = [
    'IV', 'IX', 'XL', 'XC', 'CD', 'CM'
  ];
  
  // convert s to array of chars
  var charArr = s.split('');
  var result = 0;
  var checkblock;
  var currVal;
  
  // for each char have two pointers
    // if curr char and next char then convert curr char to curr char * -1
    // add value to result
  
  for(var i = 0, j = 1, il = charArr.length; i < il; i++, j++) {
    currVal = romanNumMap[charArr[i]];
    if (j < il) {
      checkblock = charArr[i] + charArr[j];
      if (checkpoints.indexOf(checkblock) !== -1) {
        currVal = currVal * -1;
      }
    }
    
    result += currVal;
  }
  
  
  // return result
  return result;
};