Leetcode 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 

使用ASCII码一一对应

def convert_to_title(n)
    ans = ''
    while n > 0
        n -= 1
        ans = (65 + n % 26).chr + ans
        n /= 26
    end
    ans
end