171. Excel Sheet Column Number

Related to 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    AB -> 28

如题，题目可理解为二十六进制的转化。

代码如下：

public class Solution {    public int titleToNumber(String s) {        int num=0;	int[] a =new int[s.length()];	for(int j = 0; j < s.length(); j++){		a[j]=s.charAt(j)-'A'+1;		num=num+Pow(26,s.length()-j-1)*a[j];		}	return num;    }    private static int Pow(int i, int j){		if(j==0) return 1;		return i*Pow(i,j-1);	}}

或是比较灵巧的方法：如下：

public class Solution {    public int titleToNumber(String s) {        int num=0;	for(int j = 0; j < s.length(); j++){		num=num*26+s.charAt(j)-"A"+1;				}	return num;    }  }