171. 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

解题要点：

把string拆分为char数组，从后往前遍历整个数组，每一次都乘以26，依次类推。

class Solution {
    public int titleToNumber(String s) {
        int res = 0;
        int out = 1;
        char[] c = s.toCharArray();
        for(int i = c.length - 1; i >= 0; i--){
            int temp = c[i] - 'A' + 1;
            res = res + temp * out;
            out *= 26;
        }
        return res;
    }
}