Recursion

Recursion is powerful tool to solve many problems with simple and elegant code, but it is often tricky to imagine how the function calls are being made. I will try to take a problem and explain the flow of recursive calls.

Given a positive integer, return its corresponding column title as appear in an Excel sheet.

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

This problem can be solved using a recursive function and it turns out to be a single line of code.

public class ExcelTitle {
    public static String convertToTitle(int n) {
        return n == 0 ? "" : convertToTitle(--n / 26) + (char)('A' + (n % 26));

    }

    public static void main(String args[])
    {
        System.out.println(convertToTitle(27));


    }
}

The explanation is shown in the screenshot below:

The output of the call convertToTitle(27) is AA.