Binary Search Recursive Approach in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the middle index in the recursive binary search.

DSA Javascript

function binarySearch(arr, target, left, right) {
  if (left > right) return -1;
  const mid = Math.floor((left + right) [1] 2);
  if (arr[mid] === target) return mid;
  else if (arr[mid] < target) return binarySearch(arr, target, mid + 1, right);
  else return binarySearch(arr, target, left, mid - 1);
}

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of division.

Forgetting to use Math.floor which can cause decimal indices.

The middle index is found by adding left and right, then dividing by 2 using Math.floor to get an integer.

2fill in blank

medium

Complete the code to check if the target is greater than the middle element.

DSA Javascript

function binarySearch(arr, target, left, right) {
  if (left > right) return -1;
  const mid = Math.floor((left + right) / 2);
  if (arr[mid] === target) return mid;
  else if (arr[mid] [1] target) return binarySearch(arr, target, mid + 1, right);
  else return binarySearch(arr, target, left, mid - 1);
}

Drag options to blanks, or click blank then click option'

A>

B<

C===

D!==

Attempts:

3 left

💡 Hint

Common Mistakes

Using equality operator instead of comparison.

Using greater than operator which reverses the logic.

If the middle element is less than the target, search the right half by moving left to mid + 1.

3fill in blank

hard

Fix the error in the base case condition to stop recursion when the search space is invalid.

DSA Javascript

function binarySearch(arr, target, left, right) {
  if (left [1] right) return -1;
  const mid = Math.floor((left + right) / 2);
  if (arr[mid] === target) return mid;
  else if (arr[mid] < target) return binarySearch(arr, target, mid + 1, right);
  else return binarySearch(arr, target, left, mid - 1);
}

Drag options to blanks, or click blank then click option'

A>=

B<

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than which causes infinite recursion.

Using less than or equal which stops too early.

The recursion should stop when left is greater than right, meaning the target is not found.

4fill in blank

hard

Fill both blanks to complete the recursive calls for searching left and right halves.

DSA Javascript

function binarySearch(arr, target, left, right) {
  if (left > right) return -1;
  const mid = Math.floor((left + right) / 2);
  if (arr[mid] === target) return mid;
  else if (arr[mid] < target) return binarySearch(arr, target, mid [1] 1, right);
  else return binarySearch(arr, target, left, mid [2] 1);
}

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication or division instead of addition or subtraction.

Reversing the signs causing wrong search ranges.

To search the right half, increase mid by 1; to search the left half, decrease mid by 1.

5fill in blank

hard

Fill all three blanks to create a recursive binary search that returns the index or -1 if not found.

DSA Javascript

function binarySearch(arr, target, left, right) {
  if (left [1] right) return -1;
  const mid = Math.floor((left + right) / 2);
  if (arr[mid] === target) return mid;
  else if (arr[mid] [2] target) return binarySearch(arr, target, mid + 1, right);
  else return binarySearch(arr, target, left, mid [3] 1);
}

Drag options to blanks, or click blank then click option'

A>

B<

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators causing infinite recursion.

Adding instead of subtracting when searching left half.

The base case stops when left is greater than right. If middle element is less than target, search right half. Otherwise, search left half by subtracting 1 from mid.