Day 9: Iteration vs. Recursion: Analyzing Performance (Factorial)

Is Recursion better than a Loop? It depends.

Recursion is often cleaner to write and easier to read (especially for trees). But it comes at a cost: Space Complexity.

• Iteration: Uses 1 Stack Frame. It just updates a variable in a loop. Space is $O(1)$.
• Recursion: Uses N Stack Frames. If you calculate factorial(10000), you push 10,000 frames onto memory. Space is $O(N)$.

If you go too deep, recursion crashes (Stack Overflow). Iteration runs forever.

The Code

Here I implemented Factorial in both ways to compare the syntax.

// Day 9: The Two Paths

#include <stdio.h>

// Method 1: Recursive (The Elegant Way)
// Risks: Stack Overflow for large numbers
unsigned long long factorial_rec(int n) {
    if (n <= 1) return 1;
    return n * factorial_rec(n - 1);
}

// Method 2: Iterative (The Efficient Way)
// Benefits: Uses constant memory (No stack growth)
unsigned long long factorial_iter(int n) {
    unsigned long long res = 1;
    for (int i = 1; i <= n; i++) {
        res *= i;
    }
    return res;
}

int main() {
    int num = 5;
    printf("Recursive: %llu\n", factorial_rec(num));
    printf("Iterative: %llu\n", factorial_iter(num));
    return 0;
}

📂 View the source code on GitHub: https://github.com/Ujjawal0711/30-Days