Leetcode#13 Roman to Integer

 1 int transfer(char c) {
 2   switch (c) {
 3   case ‘I‘: return 1;
 4   case ‘V‘: return 5;
 5   case ‘X‘: return 10;
 6   case ‘L‘: return 50;
 7   case ‘C‘: return 100;
 8   case ‘D‘: return 500;
 9   case ‘M‘: return 1000;
10   default: return -1;
11   }
12 }
13     
14 int romanToInt(string s) {
15   int res = 0;
16   int pre = 0;
17   for (int i = 0; i < s.length(); i++) {
18     int curr = transfer(s[i]);
19     if (curr <= pre)
20       res += curr;
21     else {
22       res -= pre * 2;
23       res += curr;
24     }
25     pre = curr;
26   }
27         
28   return res;
29 }