LeetCode之Excel Sheet Column Number

1、题目

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 
     
    
  
 

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

2、分析

  

   

    

     

    
    

     

      A -> 1*26^0
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      AA -> 1*26^1 + 1*26^0
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      AAA -> 1*26^2 + 1*26^1 + 1*26^0
     
    
  
 

3、代码实现

  

   

    

     

    
    

     

      public class Solution {
     
    
   

    

     

    
    

     

       public int titleToNumber(String value) {
     
    
   

    

     

    
    

     

       if (value == null || value.length() == 0) 
     
    
   

    

     

    
    

     

      			return 0;
     
    
   

    

     

    
    

     

      		int length = value.length();
     
    
   

    

     

    
    

     

      		//A 65
     
    
   

    

     

    
    

     

      		char[] chars = value.toCharArray();
     
    
   

    

     

    
    

     

      		int result = 0;
     
    
   

    

     

    
    

     

      		int pow = 0;
     
    
   

    

     

    
    

     

      		//please here is i >= 0 not is i > 0
     
    
   

    

     

    
    

     

      		for (int i = length - 1; i >= 0; i--) {
     
    
   

    

     

    
    

     

      			int tmp = chars[i] - 'A' + 1;
     
    
   

    

     

    
    

     

      			int temp1 = (int)Math.pow(26, pow);
     
    
   

    

     

    
    

     

      			pow++;
     
    
   

    

     

    
    

     

      			result += tmp * temp1;
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     

      		return result; 
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     

      }
     
    
  
 

4、总结

注意每次写

for(int i = length - 1; i > 0 --i)
 

的时候要注意不是这样写的，需要写成这样

for(int i = length - 1; i >= 0 --i)
 

不要忘记有=号，切记，以后不要换这样的错误。

还有求^的函数要知道，不要忘记

Math.pow(26, pow)
 

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原文链接：chenyu.blog.csdn.net/article/details/68950225