[LeetCode] Problem 171 - Excel Sheet Column Number

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Given a 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

No.1

Input: “A”

Output: 1

No.2

Input: “AB”

Output: 28

No.3

Input: “ZY”

Output: 701

Code

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public int titleToNumber(String s) {
    int n = s.length() - 1;
    int sum = 0;

    for (char ch : s.toCharArray())
        sum += (ch - 'A' + 1) * Math.pow(26, n--);
    
    return sum;
}