Q: How do you flatten a nested array recursively in JavaScript?

function flatten(arr) { return arr.reduce((acc, item) => acc.concat(Array.isArray(item) ? flatten(item) : item), []); }. If an item is an array, recurse. Otherwise, concatenate.

Question 1

What is memoization in recursion in JavaScript?

Accepted Answer

Caching the results of expensive recursive calls. Before computing, check if the result is in the cache. If so, return it. This prevents redundant computation. For fibonacci, it reduces time from O(2^n) to O(n).

Question 2

How do you implement fibonacci with memoization in JavaScript?

Accepted Answer

const memo = {}; function fib(n) { if (n < 2) return n; if (memo[n]) return memo[n]; return memo[n] = fib(n-1) + fib(n-2); }. Memoization reduces time from O(2^n) to O(n).

Question 3

How do you flatten a nested array recursively in JavaScript?

Accepted Answer

function flatten(arr) { return arr.reduce((acc, item) => acc.concat(Array.isArray(item) ? flatten(item) : item), []); }. If an item is an array, recurse. Otherwise, concatenate.

Question 4

How do you traverse the DOM recursively in JavaScript?

Accepted Answer

function traverseDOM(node, callback) { callback(node); Array.from(node.children).forEach(child => traverseDOM(child, callback)); }. Call the callback on the current node, then recurse into each child.

What is memoization in recursion in JavaScript?

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