168. Excel Sheet Column Title

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

For example:

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

Example 1:

Input: 1
Output: "A"

Example 2:

Input: 28
Output: "AB"

Example 3:

Input: 701
Output: "ZY"

来自 <https://leetcode.com/problems/excel-sheet-column-title/description/>

思路1：这相当于一个26进制的转换问题，但特殊之处在于，它是从A开始到Z结束，按照题目规定A为1,Z为26，而不是一般情况下的从0到25。我们仍然可以先进行普通的26进制转换，之后再处理这一问题。 

class Solution(object):
    def convertToTitle(self, n):
        """
        :type n: int
        :rtype: str
        """
        yushu = []
        while n > 0:
            yushu.append(n % 26)
            n = n // 26
        for i in range(len(yushu)-1):
            if yushu[i] <= 0:
                yushu[i+1] = yushu[i + 1] - 1
                yushu[i] = yushu[i] + 26
        yushu=yushu[::-1]
        if yushu[0] == 0:
            del (yushu[0])
        s = ''
        for i in yushu:
            s += chr(i + 64)
        return s

 

思路2：上面的解法在逻辑上有点模糊，其实对于每一次循环n应该等于n-1因为，这样就能将1到26转换为0到25

class Solution(object):
    def convertToTitle(self, n):
        """
        :type n: int
        :rtype: str
        """
        yushu=[]
        while n>0:
            yushu.append((n-1)%26+65)
            n = (n-1)//26
        yushu=yushu[::-1]
        result=''
        for i in yushu:
            result+=chr(i)
        return result

 

思路3：对于这种重复执行问题，可以用递归方法处理

class Solution(object):
    def convertToTitle(self, n):
        """
        :type n: int
        :rtype: str
        """
        if n == 0:
            return ""
        else:
            return self.convertToTitle((n - 1) // 26)+chr((n - 1) % 26 + ord('A'))