How does recursion work in C++ for calculating Fibonacci numbers?

How does recursion work in C++ for calculating Fibonacci numbers?

Recursion in C++ allows a function to call itself. For Fibonacci, it can be defined as:

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

What are the drawbacks of using recursion for Fibonacci?

The main drawback is performance. The recursive approach has exponential time complexity, leading to many repeated calculations.

Is there a more efficient way to calculate Fibonacci numbers?

Yes, you can use dynamic programming or an iterative approach, which reduces the time complexity to linear.

Can you show me the iterative version?

Sure! Here's an iterative version:

int fibonacci(int n) {
    int a = 0, b = 1;
    for (int i = 2; i <= n; i++) {
        int c = a + b;
        a = b;
        b = c;
    }
    return n > 0 ? b : a;
}