Recursion vs Iteration When Each Wins in DSA C - Compare & Choose

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Recursive vs Iterative Factorial

What is the output of the following C code snippet that calculates factorial using recursion and iteration?

DSA C

#include <stdio.h>

int factorial_recursive(int n) {
    if (n <= 1) return 1;
    return n * factorial_recursive(n - 1);
}

int factorial_iterative(int n) {
    int result = 1;
    for (int i = 2; i <= n; i++) {
        result *= i;
    }
    return result;
}

int main() {
    int n = 5;
    printf("Recursive: %d\n", factorial_recursive(n));
    printf("Iterative: %d\n", factorial_iterative(n));
    return 0;
}

A

Recursive: 120
Iterative: 24

B

Recursive: 120
Iterative: 120

C

Recursive: 24
Iterative: 120

D

Recursive: 0
Iterative: 0

💡 Hint

Recall that factorial of 5 is 5*4*3*2*1 = 120.

Both recursive and iterative functions correctly compute factorial of 5 as 120.

🧠 Conceptual

intermediate

When is recursion preferred over iteration?

Which scenario best explains when recursion is preferred over iteration?

A When the problem can be divided into similar subproblems and has a clear base case.

B When the problem requires simple repeated addition or multiplication.

C When memory usage must be minimized and stack overflow avoided.

D When the problem involves only linear traversal of data.

💡 Hint

Think about problems like tree traversals or divide and conquer.

Recursion is best when a problem breaks down into smaller similar problems with a base case, like tree traversals or quicksort.

❓ Predict Output

advanced

Stack Overflow Risk in Recursion

What happens when the following recursive function is called with a large input like 100000?

DSA C

void recurse(int n) {
    if (n == 0) return;
    recurse(n - 1);
}

int main() {
    recurse(100000);
    return 0;
}

A Program runs infinitely without stopping.

B Program prints numbers from 100000 down to 0.

C Program causes a stack overflow error and crashes.

D Program runs successfully without errors.

💡 Hint

Consider how deep the recursion goes and stack size limits.

Deep recursion like 100000 calls exceeds typical stack size, causing stack overflow and crash.

🧠 Conceptual

advanced

Iteration advantage over recursion

Why is iteration often preferred over recursion in some cases?

A Iteration uses less memory and avoids stack overflow risks.

B Iteration is always faster than recursion in all problems.

C Iteration can solve problems that recursion cannot.

D Iteration automatically handles base cases better than recursion.

💡 Hint

Think about memory usage and function call overhead.

Iteration uses a single loop and less memory, avoiding stack overflow and overhead of recursive calls.

🚀 Application

expert

Choosing recursion or iteration for tree traversal

Given a binary tree, which approach is generally better for inorder traversal and why?

A Recursion, because iteration cannot visit nodes in order.

B Iteration, because recursion cannot be used for tree traversal.

C Iteration, because recursion always causes stack overflow in trees.

D Recursion, because it naturally follows the tree structure and is easier to implement.

💡 Hint

Think about how recursion matches the hierarchical nature of trees.

Recursion fits tree traversal naturally by visiting left subtree, node, then right subtree with simple code.