leetcode_Excel Sheet Column Number

171. 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 

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：
<span style="font-family:Menlo, Monaco, Consolas, Courier New, monospace;">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;
    }  
}</span>