168. Excel Sheet Column Title

# Easy

class Solution:
    def convertToTitle(self, n: int) -> str:
        alp = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        return self.helper(n, alp)
    
    def helper(self, n, alp): 
        if n <= 26:
            return alp[n-1]     
        ch = alp[n%26-1]
        return self.helper(n//26, alp)+ch

该怎么计算时间复杂度呢？ $O(log_{26}^n)$ ---> $O(lgn)$？ 空间复杂度也是一样的？