Find Excel column number from column title

15 Nov, 2021
We have discussed Conversion from column number to Excel Column name. In this post, reverse is discussed.Given a column title as appears in an Excel sheet, return its corresponding column number. 
column  column number
  A  ->  1
  B  ->  2
  C  ->  3
  ...
  Z  ->  26
  AA ->  27
  AB ->  28 
Examples:  
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.
 
Approach: The process is similar to binary to decimal conversion. For example, to convert AB, the formula is 26 * 1 + 2. As another example,  
To convert CDA,
3*26*26 + 4*26 + 1
= 26(3*26 + 4) + 1
= 26(0*26 + 3*26 + 4) + 1
So it is very much similar to converting binary to decimal keeping the base as 26. Take the input as string and the traverse the input string from the left to right and calculate the result as follows:  
result = 26*result + s[i] - 'A' + 1
. The result will be summation of . 
C++
Java
Python3
C#
Javascript
// C++ program to return title to result// of excel sheet.#include <bits/stdc++.h> 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 functionint main(){    cout << titleToNumber("CDA") << endl;    return 0;}
// 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 Codepublic static void main (String[] args){    System.out.print(titleToNumber("CDA"));}} // This code is contributed// by Akanksha Rai(Abby_akku)
# 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 functionprint(titleToNumber("CDA")); # This code contributed by Rajput-Ji
// 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 Codepublic static void Main(string[] args){    Console.Write(titleToNumber("CDA"));}} // This code is contributed by Shrikant13
<script> // JavaScript program to return title// to result of excel sheet. // Returns result when we pass titlefunction 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 Codedocument.write(titleToNumber("CDA")); // This code is contributed by avanitrachhadiya2155 </script>
Output:  
2133
Complexity Analysis:  
Time Complexity: O(n), where n is length of input string.
Space Complexity: O(1). As no extra space is required.
This article is contributed by Sahil Rajput. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. 
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