06_0_recursion.md

Recursion

Colloquially, recursion is the process through which a function calls itself until a base case is reached.

Some common test-questions:

Fibonacci

Output or log an array with the Fibonacci sequence until num (aka, index). More information about Fibonacci Interview Question

Solution:

function ç(num) {
  let results = [];
  if (num == 0) return [0];
  if (num == 1) return [0, 1];

  const arr = fibonacci(num - 1);
  return [...arr, arr[num - 1] + arr[num - 2]];
}

console.log(fibonacci(10));

Result:

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

Before addressing other examples, let's see HOW recursion looks in our browser's DEV tools.

• Open the Dev Tools.
• Click on Sources.
• Check or select Snippets.
• Create a New Snippet and paste the previous code (our fibonacci()).
• Then, add a breakpoint to the line return [...arr, arr[num - 1] + arr[num - 2]]; and run the snippet.

Great! So, the first time, our function is invoked with 10 as argument. The namespace result is declared initializing it with an empty array. Then, both conditionals run and since their results are false, we hit the declaration of arr which is equals to the result of invoking our function with 9 (10 - 1)

We can also add some logs to see what's going on in each iteration.

Factorial

Solution:

Result: