LeetCode (Math) Excel Sheet Column Number

Excel Sheet Column Number

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 1:

Input: "A"
Output: 1

Example 2:

Input: "AB"
Output: 28

Example 3:

Input: "ZY"
Output: 701

思路：模仿十进制数中的表示方法，利用pow（）函数来辅助计算，代码如下

class Solution {
    public int titleToNumber(String s) {
        int len = s.length();
        int res = 0;
        for (int i = 0; i < len; i++) {
            int a = (int) Math.pow(26, len -1 - i);
            int c = s.charAt(i) - 'A' + 1;
            res += a * c;
        }
        return res;
    }
}