【leetcode刷题笔记】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 

题解：其实就是一个26进制数转换成十进制数的程序：s[0]*26^(n-1)+s[1]*26^(n-2)+...+s[n-1]*26^(0)。计算的时候为了方便，从字符串最后一位开始计算，设置一个multi变量，初始值为1，每次多累加一位，就增加26倍。

Java代码如下：

 public class Solution {
     public int titleToNumber(String s) {
         int n = s.length();
         int multi = 1;
         int sum = 0;
         for(int i = n-1;i>=0;i--){
             sum += (s.charAt(i)-'A'+1)*multi;
             multi *= 26;
         }
         return sum;
     }
 }