[LeetCode] 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 

Credits:
Special thanks to @ifanchu for adding this problem and creating all test cases.

---

　　需要注意到的是不能直接 % 26，而 %26对应的字母是Z。

#include <iostream>
#include <string>
using namespace std;

class Solution {
public:
    string convertToTitle(int n) {
        if(n<1) return "";
        string ret = "";
        while(n>0){
            char a = 'A' + n%26 -1;
            if(a<'A')   a = 'Z';
            ret = a + ret;
            n= (n-1)/26;
        }
        return ret;
    }
};

int main()
{
    int n =28;
    Solution sol;
    cout<<sol.convertToTitle(n)<<endl;
    return 0;
}