从列标题中查找 Excel 列号

我们已经讨论了从列号到 Excel 列名的转换。在这篇文章中，讨论了反向。
给定出现在 Excel 工作表中的列标题，返回其对应的列号。

column  column number
  A  ->  1
  B  ->  2
  C  ->  3
  ...
  Z  ->  26
  AA ->  27
  AB ->  28 

例子：

Input: A
Output: 1
A is the first column so the output is 1.

Input: AA
Output: 27
The columns are in order A, B, ..., Y, Z, AA ..
So, there are 26 columns after which AA comes.

方法：该过程类似于二进制到十进制的转换。
例如，要转换 AB，公式为 26 * 1 + 2。
作为另一个例子，

To convert CDA,
3*26*26 + 4*26 + 1
= 26(3*26 + 4) + 1
= 26(0*26 + 3*26 + 4) + 1

所以它非常类似于将二进制转换为十进制，保持基数为 26。
将输入作为字符串，从左到右遍历输入字符串，计算结果如下：

result = 26*result + s[i] - 'A' + 1

.
结果将是总和
$Result &= \sum_{i=0}^{n} a[n-i-1]*(26^{(n-i-1)})$ .

C++

// C++ program to return title to result
// of excel sheet.
#include 
 
using namespace std;
 
// Returns result when we pass title.
int titleToNumber(string s)
{
    // This process is similar to
    // binary-to-decimal conversion
    int result = 0;
    for (const auto& c : s)
    {
        result *= 26;
        result += c  - 'A' + 1;
    }
 
    return result;
}
 
// Driver function
int main()
{
    cout << titleToNumber("CDA") << endl;
    return 0;
}

Java

// Java program to return title
// to result of excel sheet.
import java.util.*;
import java.lang.*;
 
class GFG
{
 
// Returns result when we pass title.
static int titleToNumber(String s)
{
    // This process is similar to
    // binary-to-decimal conversion
    int result = 0;
    for (int i = 0; i < s.length(); i++)
    {
        result *= 26;
        result += s.charAt(i) - 'A' + 1;
    }
    return result;
}
     
// Driver Code
public static void main (String[] args)
{
    System.out.print(titleToNumber("CDA"));
}
}
 
// This code is contributed
// by Akanksha Rai(Abby_akku)

Python3

# Python program to return title to result
# of excel sheet.
 
# Returns result when we pass title.
def titleToNumber(s):
    # This process is similar to binary-to-
    # decimal conversion
    result = 0;
    for B in range(len(s)):
        result *= 26;
        result += ord(s[B]) - ord('A') + 1;
 
    return result;
 
# Driver function
print(titleToNumber("CDA"));
 
# This code contributed by Rajput-Ji

C#

// C# program to return title
// to result of excel sheet.
using System;
 
class GFG
{
 
// Returns result when we pass title.
public static int titleToNumber(string s)
{
    // This process is similar to
    // binary-to-decimal conversion
    int result = 0;
    for (int i = 0; i < s.Length; i++)
    {
        result *= 26;
        result += s[i] - 'A' + 1;
    }
    return result;
}
 
// Driver Code
public static void Main(string[] args)
{
    Console.Write(titleToNumber("CDA"));
}
}
 
// This code is contributed by Shrikant13

Javascript

 
// JavaScript program to return title
// to result of excel sheet.
 
// Returns result when we pass title
function titleToNumber(s)
{
    // This process is similar to
    // binary-to-decimal conversion
    let result = 0;
    for (let i = 0; i < s.length; i++)
    {
        result *= 26;
        result += s[i].charCodeAt(0) - 'A'.charCodeAt(0) + 1;
    }
    return result;
}
// Driver Code
document.write(titleToNumber("CDA"));
 
// This code is contributed by avanitrachhadiya2155
 

输出：

2133

复杂性分析：

• 时间复杂度： O(n)，其中 n 是输入字符串的长度。
• 空间复杂度： O(1)。
  因为不需要额外的空间。