168. Excel Sheet Column Title

题目：

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

思路：

本题首先要了解Excel的标题性质：A~Z, AA~ZZ, AAA~ZZZ, ……；Excel的标题由A-Z字符组成，本质上是26进制的表示，因此本题就是将十进制转换成26进制

代码：

class Solution {
public:
    string convertToTitle(int n) {
        string res = "";
        while(n)
        {
            res = char((n-1)%26+ 'A') + res;
            n = (n-1)/26;
        }
        return res;
    }
};