10 Simple Recursion Problems (Java, JavaScript, Python)

Recursion becomes easy only with practice.
Here are 10 beginner-friendly problems to master recursion.

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1. Print Numbers from 1 to N

Python

def printN(n):
    if n == 0:
        return
    printN(n-1)
    print(n)

printN(5)

Java

static void printN(int n){
    if(n == 0) return;
    printN(n-1);
    System.out.println(n);
}

JavaScript

function printN(n){
    if(n === 0) return;
    printN(n-1);
    console.log(n);
}

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2. Print Numbers from N to 1

def reverse(n):
    if n == 0:
        return
    print(n)
    reverse(n-1)

static void reverse(int n){
    if(n == 0) return;
    System.out.println(n);
    reverse(n-1);
}

function reverse(n){
    if(n === 0) return;
    console.log(n);
    reverse(n-1);
}

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4. Factorial

def fact(n):
    if n == 1:
        return 1
    return n * fact(n-1)

static int fact(int n){
    if(n == 1) return 1;
    return n * fact(n-1);
}

function fact(n){
    if(n === 1) return 1;
    return n * fact(n-1);
}

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4. Sum of N Numbers

def sumN(n):
    if n == 0:
        return 0
    return n + sumN(n-1)

static int sumN(int n){
    if(n == 0) return 0;
    return n + sumN(n-1);
}

function sumN(n){
    if(n === 0) return 0;
    return n + sumN(n-1);
}

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5. Fibonacci Series

def fib(n):
    if n <= 1:
        return n
    return fib(n-1) + fib(n-2)

static int fib(int n){
    if(n <= 1) return n;
    return fib(n-1) + fib(n-2);
}

function fib(n){
    if(n <= 1) return n;
    return fib(n-1) + fib(n-2);
}

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6. Reverse a String

def reverseStr(s):
    if s == "":
        return s
    return reverseStr(s[1:]) + s[0]

static String reverseStr(String s){
    if(s.equals("")) return s;
    return reverseStr(s.substring(1)) + s.charAt(0);
}

function reverseStr(s){
    if(s === "") return s;
    return reverseStr(s.slice(1)) + s[0];
}

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7. Count Digits

def countDigits(n):
    if n == 0:
        return 0
    return 1 + countDigits(n//10)

static int countDigits(int n){
    if(n == 0) return 0;
    return 1 + countDigits(n/10);
}

function countDigits(n){
    if(n === 0) return 0;
    return 1 + countDigits(Math.floor(n/10));
}

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8. Sum of Digits

def sumDigits(n):
    if n == 0:
        return 0
    return n%10 + sumDigits(n//10)

static int sumDigits(int n){
    if(n == 0) return 0;
    return (n%10) + sumDigits(n/10);
}

function sumDigits(n){
    if(n === 0) return 0;
    return (n%10) + sumDigits(Math.floor(n/10));
}

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9. Check Palindrome (String)

def isPalindrome(s):
    if len(s) <= 1:
        return True
    return s[0] == s[-1] and isPalindrome(s[1:-1])

static boolean isPalindrome(String s){
    if(s.length() <= 1) return true;
    return s.charAt(0) == s.charAt(s.length()-1)
        && isPalindrome(s.substring(1, s.length()-1));
}

function isPalindrome(s){
    if(s.length <= 1) return true;
    return s[0] === s[s.length-1] &&
           isPalindrome(s.slice(1, -1));
}

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10. Power of a Number (xⁿ)

def power(x, n):
    if n == 0:
        return 1
    return x * power(x, n-1)

static int power(int x, int n){
    if(n == 0) return 1;
    return x * power(x, n-1);
}

function power(x, n){
    if(n === 0) return 1;
    return x * power(x, n-1);
}