Excel Sheet Column Number

Question: 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

You may view the full question here.

Approach 1: Assume a numeric system where there are 26 simple digits A-Z and the combination of these digits make numbers. In such a system, each position will have a weight of (26 * position_index). Applying this to build our solution —

//Approach 1
//Runtime: 1ms
//Memory usage: 35MB
class Solution {
    public int titleToNumber(String s) {
        int len = s.length();
        int sum = 0;
        for(int i = 0; i<len; i++){
            sum = (sum*26) + (s.charAt(i)-'A'+1);
        }
        return sum;
    }
}

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Cheers & Chao!