Find out the Excel file column number

To use recursion for solving excel file column number problem, the key idea is to break down the number using base-26 logic. We reduce the problem by continuously dividing the number by 26 and handling the remainder, which corresponds to the last letter of the column label.

Recursive Code:

java

package com.demo;   public class ExcelColumnNumber {       // Recursive function to calculate Excel column label     public static String columnNumber(int number) {         if (number <= 0) {             return ""; // Base case: Invalid input (less than 1)         }           // Adjust to 0-based indexing for correct remainder calculation         number--;                 // Recursive case: process the next character         char letter = (char) (number % 26 + 'A');         int next = number / 26;                 // Recursively process the remaining digits         return columnNumber(next) + letter;     }       public static void main(String[] args) {         // Test cases         System.out.println("Excel file column no -> " + columnNumber(90));   // Expected: "CR"         System.out.println("Excel file column no -> " + columnNumber(25));   // Expected: "Y"         System.out.println("Excel file column no -> " + columnNumber(255));  // Expected: "IV"         System.out.println("Excel file column no -> " + columnNumber(2700)); // Expected: "DVE"     } }

 

How the Recursion Works:

1. Base Case: If the number is 0 or negative, it is invalid, and the function returns an empty string.
2. Recursive Case:

ü  We convert the number from 1-based indexing (Excel format) to 0-based (which simplifies the math) by subtracting 1.

ü  The current column letter is derived by computing number % 26 + 'A' (where number % 26 gives us the correct letter from 'A' to 'Z').

ü  We recursively process the next part of the number by dividing it by 26.

3. Combining Results: At each step of recursion, the column letter is added to the result, building the final string as the recursion unwinds.

Example Execution for columnNumber(90):

Ø  90 (in Excel numbering) corresponds to "CR".

1.       columnNumber(90 - 1 = 89) → remainder is 17 ('R') and recursive call for 89 / 26 = 3.

2.       columnNumber(3 - 1 = 2) → remainder is 2 ('C') and recursive call for 2 / 26 = 0.

3.       columnNumber(0) → base case, returns "".

The results combine in reverse order, so you get "C" + "R" = "CR".

Sample Output:

Plain text

Excel file column no -> CR Excel file column no -> Y Excel file column no -> IV Excel file column no -> DVE

 

This recursive approach properly handles the conversion of numbers into Excel column labels. Let me know if you need further clarifications or modifications!