Leetcode Excel Sheet Column Number

Related to question Excel Sheet Column Title

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 

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解题思路：

很容易发现规律，例如AB = ('A'-'A' + 1) * 26 + (B-'A'+1)

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Java code:

public int titleToNumber(String s) {
        if(s == null) {
            return 0;
        }
        int sum = 0;
        for(int i = 0; i < s.length(); i++) {
            sum += (s.charAt(i) - 'A' + 1) * Math.pow(26, s.length()-1-i);
        }
        return sum;
    }