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 the time complexity of recursive fibonacci without memoization?

Accepted Answer

O(2^n) - exponential. Each call makes two recursive calls, creating a binary tree of calls. Many calls are redundant (fib(3) is computed multiple times). Memoization reduces this 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 the time complexity of recursive fibonacci without memoization?

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