Conquering the Beast: My Battle with the Complex Recursive Algorithm
Tags: javascript, programming, algorithms, webdev
Published: 2023-03-27 06:30:00

Recursion is a powerful concept in computer programming that involves breaking down a problem into smaller, more manageable parts. This approach can be particularly useful for solving complex problems, as it allows developers to build solutions incrementally, starting from the simplest cases and gradually adding more complexity.

One of the most complex recursive algorithms in JavaScript (_or TypeScript_) is known as **the Towers of Hanoi**. This algorithm is a classic example of recursive problem solving and is often used to demonstrate the power and versatility of this programming technique.

The Towers of Hanoi is a mathematical puzzle that involves moving a series of disks of different sizes from one peg to another, while following a set of rules. The rules are as follows:

1. Only one disk can be moved at a time.
2. A disk can only be moved to an empty peg or onto a disk that is larger than it.
3. The entire sequence of disks must be moved to the target peg in order to solve the puzzle.

To implement the Towers of Hanoi algorithm in JavaScript or TypeScript, we will first define a function that will represent the "move" operation. This function will take three parameters: the source peg, the target peg, and the disk size.

```typescript
function move(source: number, target: number, disk: number) {
  console.log(`Move disk ${disk} from peg ${source} to peg ${target}`);
}
```

Next, we will define the main recursive function that will solve the Towers of Hanoi puzzle. This function will take four parameters: the number of disks, the source peg, the auxiliary peg, and the target peg.

```typescript
function hanoi(n: number, source: number, aux: number, target: number) {
  if (n === 0) {
    return;
  }

  hanoi(n - 1, source, target, aux);
  move(source, target, n);
  hanoi(n - 1, aux, source, target);
}
```

The logic of this function is simple. First, it checks to see if the number of disks is zero. If it is, there is nothing left to do, so the function returns. If not, the function first calls itself with the number of disks decremented by one, moving the top n-1 disks from the source peg to the auxiliary peg. Then it calls the move function to move the nth disk from the source peg to the target peg. Finally, it calls itself again with the number of disks decremented by one, moving the n-1 disks from the auxiliary peg to the target peg.

To use this algorithm, we simply call the hanoi function with the number of disks and the source, auxiliary, and target peg numbers.

```javascript
hanoi(3, 1, 2, 3);
```

This will output the following sequence of moves:

```bash
Move disk 1 from peg 1 to peg 3
Move disk 2 from peg 1 to peg 2
Move disk 1 from peg 3 to peg 2
Move disk 3 from peg 1 to peg 3
Move disk 1 from peg 2 to peg 1
Move disk 2 from peg 2 to peg 3
Move disk 1 from peg 1 to peg 3
```

The beauty of this algorithm is its simplicity and elegance. Despite its complexity, the logic behind it is straightforward and easy to understand. This makes it an excellent example of a complex algorithm that demonstrates the power and flexibility of recursive functions.

---

This algorithm is not easy to understand at first. I had to struggle to understand it. Thanks to [TheArenaProject](https://www.thearenaproject.co/) who provided me with the tools to tackle the principles of recursion. I recommend joining the ranks of TheArenaProject Gladiators Doobs !