[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.

本质上是10进制到26进制的转换，但是1~26的映射不好操作，因此减1变成0~25的映射更好操作。

class Solution {
public:
    string convertToTitle(int n) {
        string s;
        int idx;
        while (n > 0) {
            --n;
            idx = n % 26;
            s.push_back('A' + idx);
            n /= 26;
        };
        reverse(s.begin(), s.end());
        return s;
    }
};