Excel Sheet Column Number

Given a string columnTitle that represents the column title as appear 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"].

Solution:

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