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 

Analyse：十进制转换为二十六进制，用A~Z来表示。

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

Runtime: 12ms

class Solution {
public:
    int titleToNumber(string s) {
        int result = 0;
        for(int i = s.length() - 1, j = 0; i >= 0; i--, j++){
            result += ((s[i] - 'A' + 1) * pow(26, j));
        }
        return result;
    }
};