Coursera Learner working on a presentation with Coursera logo and
Coursera Learner working on a presentation with Coursera logo and

Recursion is a brilliant tool for programming. It provides you a straightforward yet powerful solution to approach various problems. That said, recursion can sometimes be a bit complicated, especially for beginners. People often have trouble thinking recursively to see how they can approach it. Furthermore, people also find it hard to write a recursive program that does not take an excessive amount of time to run. We will discuss the fundamentals of recursion in this article, helping you refine or develop this essential programming skill.

Recursion Explained

Recursion is a method to solve problems through smaller categories of the same issue. We solve problems via the sub-problems until we arrive at its most minor version, also known as the base case. People often have trouble understanding recursion for various reasons. A recursive function keeps calling itself till it the execution stops, and a base condition becomes true. There are two parts two a recursive function:

  • The Base Case
  • The Recursive Structure

Base Case

The base is the smallest part of the problem. Surprisingly, we know the terminating condition or solution where the function could immediately return the results.

The Recursive Structure

Finding the answer to a problem through its sub-problem’s solution is a recursive structure. Once again, things get confusing as the function calls itself for breaking the present challenge to a straightforward level.

Understanding Recursion through the Countdown Problem

You must print numbers beginning from N to one in descending order. We must break the problem’s solution to find smaller versions of the issue. Therefore, it would be best to print N first and then call the function for printing the rest of the N to one number.

Printing figures from N to one equal to print (N) + Printing from N-one to one

In this example, the former is the original problem, and the latter (N-one to one is the subproblem.) You must be thinking, the functional call chain must stop somewhere, and what could the base case be?

Base Case

The countdown must conclude after the printing of one. Now, we must enter a base condition for terminating the program execution. We must now blend the base case, and recursive structure for writing the entire recursive implementation of the problem discussed earlier.

What is the Point of Using Recursion?

Recursion often shines in situations with complex problems. It would even be fair to say that it rises to the occasions when the issue is more complicated than usual. What’s more, you can apply recursion with almost any problem. However, there are particular scenarios where you will find recursion to be especially helpful. Here is a situation where recursion shines the most.

Graphs, Networks, Hierarchies

When discussing algorithms and talking about graphs, we are usually not conversing about the chart highlighting the relationship among variables such as the Top Coder rating graph (It focuses on the relationship between your rating and time.)Instead, we are mostly speaking about a web of people, things, and concepts connected in several ways.

For instance, one could imagine a road map as a graph that displays cities and their connections with the roads. Graphs can be massive, complicated, and tricky to deal with, programmatically speaking. What’s more, they are quite similar in algorithm competitions and algorithm theory. Fortunately, you can use recursion when working with complicated elements like networks and graphs.

How to Solve Problems Using Recursion?

You would be surprised to learn how much you will need to utilize your thought process for solving problems recursively. Here is an effective method you should consider as it will help you decide the base cases and recursive structure with ease:

  • How can I solve can I find a solution by finding sub-problems of a more significant issue?
  • There is no point in worrying about the sub-problem’s issue as recursion will handle it
  • Jot down a recursive structure with the correct boundary conditions and function parameter
  • Determine the base cases. As mentioned earlier, they are the smallest version of the bigger problem. You are already aware of the solutions. Also, think about the consequences of not writing a base or choosing the incorrect base.

Comprehending sub-problems and their nature are essential in recursive solutions. Here are a couple of examples:

Dynamic Programming

Solving problems through multiple sub-problems, but the sub-issues are dependent.

Divide and Conquer

Using other elements besides sub-problems, where there are independent sub-problems.

Where do People Apply Recursion

  • Designing related approximation algorithms
  • Well-recognized sorting algorithms such as Merge Sort or Quick Sort
  • Problem-solving via backtracking and exhaustive search
  • Problem-solving with the help of dynamic programming
  • Using a divide and conquer approach to solving problems
  • Finding solutions to graph problems
  • Looking for answers to tree problems
  • Solving linked and array list issues

Why Recursion is Essential

Here are some excellent reasons why recursion is beneficial for programmers and developers:

  1. Recursive solutions are mostly cleaner compared to an iterative solution. There are cases where you can reduce a `50 line to `5 to 10 recursion lines.
  2. Thinking recursively comes more naturally in some cases. Recursion is arguably the most straightforward and transparent way to solve data structure problems, e.g., trees with simple recursive structures.
  3. Some problems are quite tricky, and in some cases, impossible to solve by using Iteration.
  4. Recursion is an excellent option as it divides problems into independent, smaller sub-problems, making it simpler to parallelize.

Vital Recursion Concepts one Must Explore

  • Recursion vs. iteration comparison
  • Different recursion types and their properties
  • Using the recursion tree method to analyze recursion
  • Utilizing the Master Theorem to analyze recursion
  • Pros and cons of recursive programming
  • Understanding how to convert iterative conde into recursive code and vice versa

Why does recursion occur with stack overflow errors?

We must have a comprehensive understanding of every function to take advantage of recursion. Otherwise, we could have tons of complicated debug errors. Of course, time can be tight sometimes, but it is better to begin by writing precisely what a particular function’s role.

Recursion will be immensely helpful in the real world and Top Coder programming. You’d be surprised to see how many experienced programmers find recursion threatening. Practicing it will help you think recursively and will eventually solve tricky programming problems.