168. Excel Sheet Column Title & 171. Excel Sheet Column Numb

"""
168. Excel Sheet Column Title & 171. Excel Sheet Column Number
这两道题其实是一道题。
想法其实在这个讨论的帖子里面。 https://leetcode.com/problems/excel-sheet-column-title/discuss/51404/Python-solution-with-explanation

Now we can see that ABCD＝A×26³＋B×26²＋C×26¹＋D＝1×26³＋2×26²＋3×26¹＋4
But how to get the column title from the number? We can't simply use the n%26 method because:
ZZZZ＝Z×26³＋Z×26²＋Z×26¹＋Z＝26×26³＋26×26²＋26×26¹＋26
We can use (n-1)%26 instead, then we get a number range from 0 to 25.
"""
"""
168. Excel Sheet Column Title 这道题的难点在于不能 n % 26 要用 (n-1) % 26
"""
class Solution:
    def __init__(self):
        self.apl = {}
        self.w = 65
        for i in range(0, 26):
            self.apl[i] = chr(self.w)
            self.w += 1

    def convertToTitle(self, n):
        """
        :type n: int
        :rtype: str
        """
        res = ""
        while n > 0:
            tmp = self.apl[(n-1) % 26]
            res = tmp + res
            n = (n-1) // 26

        return res

"""
171. Excel Sheet Column Number
这道题就是反向求一个 26 进制的数字 => 10进制的数字
ABCD＝A×26³＋B×26²＋C×26¹＋D＝1×26³＋2×26²＋3×26¹＋4
"""
class Solution:
    def __init__(self):
        self.apl = {}
        self.c = 65
        for i in range(1, 27):
            self.apl[chr(self.c)] = i
            self.c += 1

    def titleToNumber(self, s: str) -> int:
        res = 0
        p = len(s) - 1
        i = 0
        while i < len(s):
            tmp = self.apl[s[p-i]]
            res += tmp * (26**i)
            i += 1

        return res