Recursion in Java → VTULOOP

Recursion Definition – Recursion is a technique in programming language, where the function calls itself directly or indirectly is called Recursion.

In this blog, I have added beginner-level examples of recursion.

Table of Contents

Breakdown of Recursive Algorithm

Every recursive algorithm follows the below steps

Contains Base Case(Stopping point for the algorithm).
Work toward the case.
Recursively calling itself until it reaches the base case.

5 Beginner Level Recursion Problems.

If you are a beginner to recursion then the following are the very simple and easy level problems that you must know before jumping into Leetcode or GFG.

1] Factorial of Number

Logic

Declared a mul variable outside the recursion method otherwise, it will also be changed to the initial value once the recursive method calls itself.
Added the main logic of how the factorial of a number is calculated.
Added the base condition, when the n value becomes 0 or 1 returning the factorial(mul).
For each recursive call of method keep decrementing the value of n.
Calling the method recursively.

package Recursion;

public class FactorialNumber {
    public static void main(String[] args) {
        int n=5;
        System.out.println(fact(n));
    }
    public static int mul=1;
    public static int fact(int n){
        mul=mul*(n);
        if(n==0||n==1){
            return mul;
        }
        n--;
        return fact(n);
    }
}

2] Fibonacci Series of Number

package Recursion;

public class FibonacciSeries {
    public static void main(String[] args) {
        System.out.println(0);
        System.out.println(1);
        System.out.println(fibonacciSeries(10));
    }
    public static int start=0;
    public static int prev=1;
    public static  int current=1;
    public static int fibonacciSeries(int n){
        if(n-3==0){
            current=start+prev;
            return current;
        }
        current=start+prev;
        start=prev;
        prev=current;
        n--;
        System.out.println(current);
        return fibonacciSeries(n);
    }
}

3] Palindrome

package Recursion;

public class PalindromeUsingRecursion {
    public static void main(String[] args) {
        String s="abbbba";
        System.out.println(checkPalin(s));
    }
    public static boolean checkPalin(String s){
        if(s.length()==0 || s.length()==1){
            return true;
        }
        if(s.charAt(0)==s.charAt(s.length()-1)){
            return checkPalin(s.substring(1,s.length()-1));
        }
        return false;
    }
}

4] Print N numbers in Increasing Order

package Recursion;

public class PrintnNumbers {
    public static void main(String[] args) {
        int n=10;
        System.out.println(printNumbersIncreasingOrder(n));
    }
    public static int start=0;

    public static int printNumbersIncreasingOrder(int n){
        if(start+1==n){
            start++;
            return start;
        }
        start++;
        System.out.println(start);
        return printNumbersIncreasingOrder(n);
    }
}

5] Print N numbers in Decreasing Order

package Recursion;

public class PrintnNumbers {
    public static void main(String[] args) {
        int n=10;
        System.out.println(printNumbersDecreasingOrder(n));
    }
    public static int printNumbersDecreasingOrder(int n){
        if(n==1){
            return n;
        }
        System.out.println(n);
        n--;
        return printNumbersDecreasingOrder(n);
    }
}