Recursion Interview Questions in JavaScript

Recursion Interview Questions

Q1: Implement factorial.

function factorial(n) { if (n <= 1) return 1; return n * factorial(n - 1); }

Q2: Implement fibonacci with memoization.

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);
}

Q3: Flatten a nested array.

function flatten(arr) {
  return arr.reduce((acc, item) => acc.concat(Array.isArray(item) ? flatten(item) : item), []);
}

Q4: Traverse a DOM tree.

function traverseDOM(node, callback) {
  callback(node);
  node.children.forEach(child => traverseDOM(child, callback));
}

Q5: Implement a countdown.

function countdown(n) {
  if (n < 0) return;
  console.log(n);
  countdown(n - 1);
}

The Takeaway

Recursion interview questions: factorial (base case + n * recurse), fibonacci with memoization (cache results), flatten (reduce + recurse on arrays), DOM traversal (recurse on children), and countdown (base case + recurse with n-1).