🌀 Recursion¶

Prerequisites: None

Recursion is when a function calls itself. It is a powerful but tricky concept that requires a clear Base Case to prevent infinite loops.

1. Factorial using Recursion¶

Rating: Beginner | Difficulty: Easy Calculate n! using a recursive function.

💡 Hint

Base case:

if (n <=
1) return 1

. Recursive case: return n * fact(n - 1).

2. Sum of Natural Numbers¶

Rating: Beginner | Difficulty: Easy Find the sum of numbers from 1 to N using recursion.

💡 Hint

sum(n) =
n + sum(n - 1)

.

3. Fibonacci Sequence (Recursive)¶

Rating: Beginner | Difficulty: Easy Find the Nth Fibonacci number using recursion.

💡 Hint

fib(n) = fib(n -
1) + fib(n - 2)

. Base cases: n=0 or n=1.

4. Power of a Number (Recursive)¶

Rating: Intermediate | Difficulty: Medium Calculate base^exponent using recursion.

💡 Hint

power(b, e) = b *
power(b, e - 1)

. Base case: e = 0.

5. Sum of Digits (Recursive)¶

Rating: Intermediate | Difficulty: Medium Extract and sum digits of a number using recursion.

💡 Hint

return (num
% 10) + sumDigits(num / 10)

.

6. Reverse a String (Recursive)¶

Rating: Intermediate | Difficulty: Medium Print a string in reverse using a recursive function.

💡 Hint

Print the last character first, then call the function for the rest of the string.

7. Count Digits¶

Rating: Beginner | Difficulty: Easy Count how many digits are in a number using recursion.

💡 Hint

return 1
+ count(n / 10)

. Base case: n < 10.

8. GCD using Recursion¶

Rating: Advanced | Difficulty: Medium Implement the Euclidean algorithm recursively to find the Greatest Common Divisor.

💡 Hint

gcd(a, b) = gcd(b, a % b). Base case: b == 0.

9. Palindrome Check (Recursive)¶

Rating: Advanced | Difficulty: Medium Check if a string is a palindrome using recursion.

💡 Hint

Check if first == last, then recurse for the inner substring.

10. Binary Search (Recursive)¶

Rating: Advanced | Difficulty: Hard Implement Binary Search on a sorted array using recursion.

💡 Hint

Find mid. If key < mid, search left half; else search right half.

11. Array Traversal¶

Rating: Intermediate | Difficulty: Medium Print all elements of an array recursively.

💡 Hint

Pass the array and the current index to the function.

12. Decimal to Binary (Recursive)¶

Rating: Advanced | Difficulty: Medium Convert a decimal integer to its binary equivalent using recursion.

💡 Hint

Print n % 2 after the recursive call convert(n / 2).

13. Towers of Hanoi¶

Rating: Pro | Difficulty: Hard Solve the Towers of Hanoi puzzle for N disks.

💡 Hint

The classic recursion problem! Move n-1 disks from A to B using C, move disk n to C, then move n-1 disks from B to C using A.

14. Find Max in Array (Recursive)¶

Rating: Advanced | Difficulty: Medium Find the maximum element in an array using recursion.

💡 Hint

max(arr[n]) = compare(arr[n-1], max(arr, n-1)).

15. All Permutations of a String¶

Rating: Pro | Difficulty: Hard Generate and print all possible permutations of a given string (e.g., "abc").

💡 Hint

Swap characters and recurse for the remaining part of the string.

← Previous: Functions | Next Topic: File Handling →