Convert base10/demical number n into "base26" string.

(Note that there is **no "zero"** in A~Z, thus we regard it base26 instead of base27).

1~26 represent A~Z separately. 27 represents "AA".

While in common presentation of baseX(binary, octal, ...), 27 should represent "A0".

The peoblem can be easily solved by iteration of "mod 26 and divided by 26".

```
class Solution {
public:
string convertToTitle(int n) {
if(n < 1)
return "";
else
{
string result = "";
while(n)
{//get every letter in n from right to left
n --;
char c = n%26 + 'A';
result += c;
n /= 26;
}
reverse(result.begin(), result.end());
return result;
}
}
};
```