[LeetCode][JavaScript]Roman to Integer

Roman to Integer

Given a roman numeral, convert it to an integer.

Input is guaranteed to be within the range from 1 to 3999.

https://leetcode.com/problems/roman-to-integer/

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罗马数字转阿拉伯数字。

从后往前扫，如果当前的数大于之前的数，加上这个数，反之减去当前的数。

/**
 * @param {string} s
 * @return {number}
 */
var romanToInt = function(s) {
    var map = {};
    map["I"] = 1; map["V"] = 5; map["X"] = 10; map["L"] = 50;
    map["C"] = 100; map["D"] = 500; map["M"] = 1000;
    var res, tmp = 0;
    for(var i = s.length - 1; i >= 0; i--){
        if(!res){
            res = map[s[i]];
            continue;
        }
        if(map[s[i]] >= map[s[i + 1]]){
            res += map[s[i]];
        }else{
            res -= map[s[i]];
        }
    }
    return res;
};