### Question

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.

### Analysis

This is pretty much a similar question. It’s pretty easy.

### Code

```
public class Solution {
public int titleToNumber(String s) {
if (s == null || s.length() == 0) {
return 0;
}
int sum = 0;
for (char ch: s.toCharArray()) {
sum *= 26;
sum += (int) (ch - 'A' + 1);
}
return sum;
}
}
```