leetcode 13. Roman to Integer

Given a roman numeral, convert it to an integer.

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

Roman Numerals Chart

						M=1000			D = 500
I	1		XXXII	32		LXIII	63		XCIV	94
II	2		XXXIII	33		LXIV	64		XCV	95
III	3		XXXIV	34		LXV	65		XCVI	96
IV	4		XXXV	35		LXVI	66		XCVII	97
V	5		XXXVI	36		LXVII	67		XCVIII	98
VI	6		XXXVII	37		LXVIII	68		XCIX	99
VII	7		XXXVIII	38		LXIX	69		C	100
VIII	8		XXXIX	39		LXX	70
IX	9		XL	40		LXXI	71		EX.
X	10		XLI	41		LXXII	72		DI	501
XI	11		XLII	42		LXXIII	73		DL	550
XII	12		XLIII	43		LXXIV	74		DXXX	530
XIII	13		XLIV	44		LXXV	75		DCCVII	707
XIV	14		XLV	45		LXXVI	76		DCCCXC	890
XV	15		XLVI	46		LXXVII	77		MD	1500
XVI	16		XLVII	47		LXXVIII	78		MDCCC	1800
XVII	17		XLVIII	48		LXXIX	79		CM	900
XVIII	18		XLIX	49		LXXX	80
XIX	19		L	50		LXXXI	81
XX	20		LI	51		LXXXII	82
XXI	21		LII	52		LXXXIII	83
XXII	22		LIII	53		LXXXIV	84
XXIII	23		LIV	54		LXXXV	85
XXIV	24		LV	55		LXXXVI	86
XXV	25		LVI	56		LXXXVII	87
XXVI	26		LVII	57		LXXXVIII	88
XXVII	27		LVIII	58		LXXXIX	89
XXVIII	28		LIX	59		XC	90
XXIX	29		LX	60		XCI	91
XXX	30		LXI	61		XCII	92
XXXI	31		LXII	62		XCIII	93

其实看明白这个该死的表就可以求解了！

class Solution(object):
    def romanToInt(self, s):
        """
        :type s: str
        :rtype: int
        """
        roman = {'M': 1000,'D': 500 ,'C': 100,'L': 50,'X': 10,'V': 5,'I': 1}
        nums = [roman[c] for c in s]
        ans = 0
        for i in xrange(0, len(s)-1):
            if nums[i] < nums[i+1]:
                ans -= nums[i]
            else:
                ans += nums[i]
        return ans + nums[-1]