For example:
​
    1 -> A
    2 -> B
    3 -> C
    ...
    26 -> Z
    27 -> AA
    28 -> AB 
    ...
Example 1:
​
Input: 1
Output: "A"
Example 2:
​
Input: 28
Output: "AB"
Example 3:
​
Input: 701
Output: "ZY"

class Solution {
public:
    string convertToTitle(int n) {
        string res;
        while(n>26)
        {
            int t=(n-1)%26;
            cout<<t<<endl;
            res= char('A'+t) +res;
            n=(n-t)/26;
        }
    //    cout<<n<<endl;
        return char('A' +n-1) + res;
    }
};