LeetCode#171 Excel Sheet Column Number

Problem Definition:

　　Given a column title as appear in an Excel sheet, return its corresponding column number.

　　For example:

　　　　A -> 1　　B -> 2 　　C -> 3 ...　　 Z -> 26 　　AA -> 27 　　 AB -> 28
Solution:

def titleToNumber( s):
    s=s[::-1]
    num=0
    for i,c in enumerate(s):
        num+=(ord(c)-64)*(26**i)
    return num

Use reduce:

def titleToNumber( s):
       return reduce(lambda x,y: x*26+y, (ord(c)-64 for c in s))

Well... the efficiency is not quite as good as expected, specious huh...