leetcode之Excel Sheet Column Number

这个excel sheet column number就是一个26进制数。代码如下：

class Solution(object):
def titleToNumber(self, s):
"""
:type s: str
:rtype: int
"""
dic = {'A': 1, 'B': 2, 'C': 3, 'D': 4, 'E': 5, 'F': 6, 'G': 7, 'H': 8, 'I': 9, 'J': 10, 'K': 11, 'L': 12, 'M': 13, 'N': 14, 'O': 15, 'P': 16, 'Q': 17, 'R': 18, 'S': 19, 'T': 20, 'U': 21, 'V': 22, 'W':23, 'X': 24, 'Y': 25, 'Z':26}
if s == '':
return 0
a = len(s)
n = 0
for i in range(a):
# print i
n = dic[s[i]] * (26 ** (a - 1 - i)) + n
# print n
return n