leetcode-13-Roman to Integer

1.说明：

    题目要求将罗马数字转为阿拉伯数字。思路是从个位开始，匹配各个位的数字，一直到最高位为止。需要注意两点，第一是要移除已经匹配完的数字，防止在匹配更高位数字时产生歧义。第二是在匹配的时候，为防止歧义，应遵循一定顺序，比如应先匹配4，6，7，8然后再匹配5。

2.代码：

/** * @param {string} s * @return {number} */var romanToInt = function(s) {    var num = 0;    var list = [        {            grade: 1,            one: 'I',            five: 'V'        },        {            grade: 10,            one: 'X',            five: 'L'        },        {            grade: 100,            one: 'C',            five: 'D'        },        {            grade: 1000,            one: 'M'        }    ];    var map = function (cur, next) {        var result = 0;        var one = cur.one;        var five = cur.five;        var ten = next && next.one;        var nine = ten ? (one + ten) : 'doomliu';        var fiveIndex = s.indexOf(five);        var oneIndex = s.indexOf(one);        var nineIndex = s.indexOf(nine);        if (nineIndex !== -1) {            s = s.slice(0, nineIndex);            result = 9;        }        else if (fiveIndex !== -1) {            var preIndex = postIndex = fiveIndex;            while (preIndex >= 0 && (s[--preIndex] === one)) { }            while (postIndex <= s.length - 1 && (s[++postIndex] === one)) { }            s = s.slice(0, preIndex + 1);            result = 5 + ((postIndex - 1) + (preIndex + 1) - 2 * fiveIndex);        }        else if (oneIndex !== -1) {            var postIndex = oneIndex;            while (postIndex <= s.length - 1 && s[++postIndex] === one) { }            s = s.slice(0, oneIndex);            result = (postIndex - 1) - oneIndex + 1;        }        result *= cur.grade;        return result;    };    while (list.length) {        num += map(list[0], list[1]);        list.shift();    }    return num;};