leetcode 13. Roman to Integer

var romanToInt = function(s) {
    var dct = {};
    dct['I'] = 1;
    dct['i'] = 1;
    dct['V'] = 5;
    dct['v'] = 5;
    dct['X'] = 10;
    dct['x'] = 10;
    dct['L'] = 50;
    dct['l'] = 50;
    dct['C'] = 100;
    dct['c'] = 100;
    dct['D'] = 500;
    dct['d'] = 500;
    dct['M'] = 1000;
    dct['m'] = 1000;

    var sum = 0, j;
    for(var i = 0; i < s.length; ++i) {
        j = i+1;

        if(j < s.length && dct[s[j]] > dct[s[i]]) {
            sum += dct[s[j]] - dct[s[i]];
            i = j;
        }
        else {
            sum += dct[s[i]];
        }
    }
    return sum;
};