Recursion

Some data nests inside more data. In script.js, write functions that solve a smaller version of the problem until they reach a stopping case; inspect the Console to check each result.

Recursion is when a function calls itself to solve a smaller version of the same problem. Every recursive solution needs:

1. Base case — the simplest input that can be answered directly (stops the recursion).
2. Recursive case — breaks the problem into a smaller sub-problem.

A base case in a nested structure

function countBoxes(box) {
  if (!box.children) return 1;
  return 1 + box.children.reduce((total, child) => total + countBoxes(child), 0);
}

console.log(countBoxes({ children: [{}, { children: [{}] }] }));

The object with no children stops the calls; each parent counts itself and its children. For a simpler linear example, a sum removes one item at a time:

function sum(arr) {
    if (arr.length === 0) return 0;
    return arr[0] + sum(arr.slice(1));
}

For power(base, exp), stop at exponent 0; otherwise multiply by the result for exp - 1. For flatten(arr), walk each item: recurse only when that item is an array, and append plain values to the result. An empty array returns an empty result. These are the two distinct base cases you will need below.