Find Excel column name from a given column number

MS Excel columns has a pattern like A, B, C, …, Z, AA, AB, AC, …., AZ, BA, BB, … ZZ, AAA, AAB ….. etc. In other words, column 1 is named as “A”, column 2 as “B”, column 27 as “AA”.

Given a column number, find its corresponding Excel column name. Following are more examples.

Input          Output
 26             Z
 51             AY
 52             AZ
 80             CB
 676            YZ
 702            ZZ
 705            AAC

Thanks to Mrigank Dembla for suggesting the below solution in a comment.

Suppose we have a number n, let’s say 28. so corresponding to it we need to print the column name. We need to take remainder with 26.

If remainder with 26 comes out to be 0 (meaning 26, 52 and so on) then we put ‘Z’ in the output string and new n becomes n/26 -1 because here we are considering 26 to be ‘Z’ while in actual it’s 25th with respect to ‘A’.



Similarly if the remainder comes out to be non zero. (like 1, 2, 3 and so on) then we need to just insert the char accordingly in the string and do n = n/26.

Finally we reverse the string and print.

Example:
n = 700

Remainder (n%26) is 24. So we put ‘X’ in output string and n becomes n/26 which is 26.

Remainder (26%26) is 0. So we put ‘Z’ in output string and n becomes n/26 -1 which is 0.

Following is C++ implementation of above approach.

C++

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// C++ program to find Excel
// column name from a given
// column number
#include <bits/stdc++.h>
#define MAX 50
using namespace std;
  
// Function to print Excel column name for a given column number
void printString(int n)
{
    char str[MAX]; // To store result (Excel column name)
    int i = 0; // To store current index in str which is result
  
    while (n > 0) {
        // Find remainder
        int rem = n % 26;
  
        // If remainder is 0, then a 'Z' must be there in output
        if (rem == 0) {
            str[i++] = 'Z';
            n = (n / 26) - 1;
        }
        else // If remainder is non-zero
        {
            str[i++] = (rem - 1) + 'A';
            n = n / 26;
        }
    }
    str[i] = '\0';
  
    // Reverse the string and print result
    reverse(str, str + strlen(str));
    cout << str << endl;
  
    return;
}
  
// Driver program to test above function
int main()
{
    printString(26);
    printString(51);
    printString(52);
    printString(80);
    printString(676);
    printString(702);
    printString(705);
    return 0;
}

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Java

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// Java program to find Excel
// column name from a given
// column number
  
public class ExcelColumnTitle {
    // Function to print Excel column
    // name for a given column number
    private static void printString(int columnNumber)
    {
        // To store result (Excel column name)
        StringBuilder columnName = new StringBuilder();
  
        while (columnNumber > 0) {
            // Find remainder
            int rem = columnNumber % 26;
  
            // If remainder is 0, then a
            // 'Z' must be there in output
            if (rem == 0) {
                columnName.append("Z");
                columnNumber = (columnNumber / 26) - 1;
            }
            else // If remainder is non-zero
            {
                columnName.append((char)((rem - 1) + 'A'));
                columnNumber = columnNumber / 26;
            }
        }
  
        // Reverse the string and print result
        System.out.println(columnName.reverse());
    }
  
    // Driver program to test above function
    public static void main(String[] args)
    {
        printString(26);
        printString(51);
        printString(52);
        printString(80);
        printString(676);
        printString(702);
        printString(705);
    }
}
  
// This code is contributed by Harikrishnan Rajan

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Python

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# Python program to find Excel column name from a 
# given column number
  
MAX = 50
  
# Function to print Excel column name 
# for a given column number
def printString(n):
  
    # To store result (Excel column name)
    string = ["\0"] * MAX
  
    # To store current index in str which is result
    i = 0
  
    while n > 0:
        # Find remainder
        rem = n % 26
  
        # if remainder is 0, then a 
        # 'Z' must be there in output
        if rem == 0:
            string[i] = 'Z'
            i += 1
            n = (n / 26) - 1
        else:
            string[i] = chr((rem - 1) + ord('A'))
            i += 1
            n = n / 26
    string[i] = '\0'
  
    # Reverse the string and print result
    string = string[::-1]
    print "".join(string)
  
# Driver program to test the above Function
printString(26)
printString(51)
printString(52)
printString(80)
printString(676)
printString(702)
printString(705)
  
# This code is contributed by BHAVYA JAIN

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Output

Z
AY
AZ
CB
YZ
ZZ
AAC

Method 2
The problem is similar to converting a decimal number to its binary representation but instead of binary base system where we have two digits only 0 and 1, here we have 26 characters from A-Z .



So, we are dealing with base 26 instead of base binary.

That’s not where the fun ends, we don’t have zero in this number system, as A represents 1, B represents 2 and so on Z represents 26.

To make the problem easily understandable, we approach the problem in two steps:

  1. Convert the number to base 26 representation, considering we have 0 also in the system.
  2. Change the representation to the one without having 0 in its system.

HOW? Here is an example

Step 1:
Consider we have number 676, How to get its representation in base 26 system ? Same way we do for binary system, Instead of division and remainder by 2, we do division and remainder by 26.

Base 26 representation of 676 is : 100 

Step2

But Hey, we can’t have zero in our representation. right? Because its not part of our number system. How do we get rid of zero? Well its simple, but before doing that lets remind one simple math trick:


Subtraction: 
5000 - 9, How do you subtract 9 from 0 ? You borrow
from next significant bit, right.  

  • In decimal number system to deal with zero we borrow 10, and subtract 1 from next significant.
  • In Base 26 Number System to deal with zero we borrow 26 and subtract 1 from next significant bit.

So Convert 10026 to number system which does not have ‘0’, we get (25 26)26
Symbolic representation of the same is : YZ

Here is the C++ Implementation of the same:

C++

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#include <iostream>
using namespace std;
  
void printString(int n)
{
    int arr[10000];
    int i = 0;
  
    // Step 1: Converting to number assuming
    // 0 in number system
    while (n) {
        arr[i] = n % 26;
        n = n / 26;
        i++;
    }
  
    // Step 2: Getting rid of 0, as 0 is
    // not part of number system
    for (int j = 0; j < i - 1; j++) {
        if (arr[j] <= 0) {
            arr[j] += 26;
            arr[j + 1] = arr[j + 1] - 1;
        }
    }
  
    for (int j = i; j >= 0; j--) {
        if (arr[j] > 0)
            cout << char('A' + arr[j] - 1);
    }
  
    cout << endl;
}
  
// Driver program to test above function
int main()
{
    printString(26);
    printString(51);
    printString(52);
    printString(80);
    printString(676);
    printString(702);
    printString(705);
    return 0;
}
  
// This code is contributed by Ankur Goel

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Related Article :
Find Excel column number from column title

This article is contributed by Kartik. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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