[LeetCode]171. Excel Sheet Column Number

题目描述：

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 

思路：

和168题是互逆的，从26进制转10进制
s.charAt(i)-'A'是为了算出s中第i位对应的相对值
可以省去强制转化(int)类型

public class Solution171 {
    public int titleToNumber(String s) {
        int sum = 0;
        for(int i = 0; i < s.length();i++){
            sum = 26 * sum + s.charAt(i) - 'A'+1;            
        }    
        return sum;
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Solution171 solution171 = new Solution171();
        String s = "AB";
        System.out.println(solution171.titleToNumber(s));
    }

}