Advantages and Disadvantages of Recursion

Advantages of Recursion

Let’s discuss the advantages first.

1.  Simplifies code for complex problems

Some problems can naturally be solved through recursion. For example, we learned how to find the factorial of a number through recursion. We saw how we can directly use the formula of factorial of a number within the program, and the program was able to apply the formula correctly to solve the problem. The solution just came out naturally. Similarly, there are many other problems where recursion solves the problem easily like solving the puzzle called Towers of Hanoi, generating permutations and combinations, etc.

2.   Elegant in solving problems based on divide and conquer strategy

Divide and conquer strategy is quite popular in algorithms to solve some interesting problems like sorting numbers (popular algorithms like merge sort and quick sort are used to sort numbers), fast multiplication using Karatsuba multiplication algorithm, finding minimum and maximum in a list of items, and so on. All these problems can easily be solved recursively because the divide and conquer, as the name suggests, is based on the basic principle of recursion–divide the problem into smaller problems and conquer them. Simple 😀

3.  Reduced code size

Recursive solutions to problems require fewer lines of code compared to their iterative counterparts making the code more readable.

For example, the problem of finding the nth Fibonacci number can be solved iteratively as follows:

int fibonacci_iterative(int n) {
    int a = 0, b = 1, next;
    if (n == 0) {
        return a;
    }
    for (int i = 2; i <= n; i++) {
        next = a + b;
        a = b;
        b = next;
    }
    return b;
}

The concise recursive solution to the same problem is as follows:

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

The difference is clear.

Disadvantages of Recursion

Recursion is not without disadvantages. Let’s see what they are.

1.  Performance overhead

Recursion causes performance overhead due to increased function calls compared to its iterative counterparts. Performance overhead refers to the additional resource consumption, such as memory and time, required to manage function calls. When a function is called, its activation record goes inside the call stack with additional information such as return address, local variables, etc. When a function completes its execution, the associated activation record must be removed from the call stack. This back-and-forth operation consumes time and processing power. Not only this, each activation record occupies some area of memory. In a recursive procedure, there can be a lot of function calls for finding the result. For example, the factorial of some large number may need a lot of function calls which leads to a large number of activation records in the call stack. Therefore, there will be a lot of memory consumption, and hence memory overhead. 

So, to summarize, recursion leads to performance overhead due to the large number of function calls compared to their iterative versions where probably one or two function calls are needed.

2.  Risk of stack overflow

If the depth of recursion (the number of activation records at any point of time) becomes too large, then it can lead to stack overflow. 

Picture this: you have a jar filled with water, and you keep adding more water. What happens? It overflows, right? Well, the same thing can happen with a call stack. If you have too many activation records, it’s like trying to pour more water into an already full jar. The call stack can’t handle it, and it overflows.

3.  Lack of iterative alternative

Not every recursive problem has a straightforward iterative solution. This can be a problem as the iterative solution is always preferred over the recursive solution if performance and efficiency is a concern.

Conclusion

Recursion is a useful tool for solving complex problems by breaking them down into smaller problems, but it comes with some trade-offs including performance issues and the risk of stack overflow. Understanding when to use recursion and when to opt for an iterative solution is the key to writing efficient and maintainable code.