[LeetCode]013. Roman to Integer

今日問題をする時leetcodeが改版したことを発見して、コンパイルして提出した後にすべてのtest casesを見ることができます.
leetcodeの作者はまだ華人で、かなり力があります!
Given a roman numeral, convert it to an integer.
Input is guaranteed to be within the range from 1 to 3999.
Solution: 
The concept of roman numerals.
この解法の鍵は,特殊な数字の表現(すなわち,減算:9=10−1,90=100−10,40=50−10.etc)が2文字の間にしか存在しないことにある.残りは加算されます.

public class Solution {
    public int charToNum (char c){
        switch(c){
            case 'I': return 1;
            case 'V': return 5;
            case 'X': return 10;
            case 'L': return 50;
            case 'C': return 100;
            case 'D': return 500;
            case 'M': return 1000;
            default: return 0;
        }
    }
    public int romanToInt(String s) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(s==null || s.length() <= 0){
            return 0;
        }
        int result = 0;
        int pos = s.length() - 1;
        while(pos >= 0){
            if(pos-1 >= 0 && charToNum(s.charAt(pos)) > charToNum(s.charAt(pos-1))){
                result += charToNum(s.charAt(pos)) - charToNum(s.charAt(pos-1));
                pos -= 2;
            }else{
                result += charToNum(s.charAt(pos));
                pos--;
            }
        }
        return result;
    }
}

2015-04-15 update python solution:

class Solution:
    # @param s, a string
    # @return an integer
    def romanToInt(self, s):
        romanDict = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
        length = len(s)
        if length == 1:
            return romanDict[s]
        result = romanDict[s[0]]
        for i in range(1, length):
            if romanDict[s[i]] > romanDict[s[i-1]]:
                result = result - romanDict[s[i-1]] + (romanDict[s[i]] - romanDict[s[i-1]])
            else:
                result += romanDict[s[i]]
        return result

s = Solution()
print s.romanToInt('M') == 1000
print s.romanToInt('MMM') == 3000
print s.romanToInt('MMMXXX') == 3030
print s.romanToInt('MMMCMXCIX') == 3999
print s.romanToInt('MMMCMXCVIII') == 3998
print s.romanToInt('MI') == 1001
print s.romanToInt('MMMIII') == 3003
print s.romanToInt('IV') == 4
print s.romanToInt('MMIX') == 2009
print s.romanToInt('MMMCDXLIX') == 3449