Given a string `columnTitle` that represents the column title as it appears in an Excel sheet, return its corresponding column number.
For example:
```
A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28
...
```
Example 1
Input:columnTitle = "A"
Output:1
Example 2
Input:columnTitle = "AB"
Output:28
Example 3
Input:columnTitle = "ZY"
Output:701
Constraints
- 1 <= columnTitle.length <= 7
- columnTitle consists only of uppercase English letters.
- columnTitle is in the range ["A", "FXSHRXW"].