Excel column number from column title

Given a column title as appears in an Excel sheet, return its corresponding column number.

The following are example column numbers for given column names.

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

Examples: 

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

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

Base-26 to Decimal - O(n) Time and O(1) Space

The process is similar to binary to decimal conversion. Treat the Excel column title as a base-26 number, where A = 1, B = 2, ..., Z = 26.  For example, to convert AB, the formula is 26 * 1 + 2.

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

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

// C++ program to return title to result
// of excel sheet.
#include <bits/stdc++.h>

using namespace std;

// Returns result when we pass title.
int excelColumnNumber(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 << excelColumnNumber("CDA") << endl;
    return 0;
}

// Java program to return title
// to result of excel sheet.
import java.lang.*;
import java.util.*;

class GFG {

    // Returns result when we pass title.
    static int excelColumnNumber(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(excelColumnNumber("CDA"));
    }
}    
    

# Python program to return title to result 
# of excel sheet. 

# Returns result when we pass title. 
def excelColumnNumber(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(excelColumnNumber("CDA")); 

// C# program to return title 
// to result of excel sheet. 
using System;

class GFG
{

// Returns result when we pass title. 
public static int excelColumnNumber(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(excelColumnNumber("CDA"));
}
}

// Function to convert Excel column title to number
function excelColumnNumber(s) {
    let result = 0;

    for (let i = 0; i < s.length; i++) {
        result = result * 26 + (s.charCodeAt(i) - 'A'.charCodeAt(0) + 1);
    }

    return result;
}

// Driver Code
console.log(excelColumnNumber("CDA")); 

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