Convert Sorted Array to Balanced BST in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find the middle index of the array.

DSA Javascript

const mid = Math.[1]((start + end) / 2);

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Aabs

Bfloor

Cround

Dceil

Attempts:

3 left

💡 Hint

Common Mistakes

Using Math.ceil causes index to go out of range.

Using Math.round can pick wrong middle for even length arrays.

We use Math.floor to get the middle index as an integer by rounding down.

2fill in blank

medium

Complete the code to create a new tree node with the middle element.

DSA Javascript

const node = new TreeNode([1][mid]);

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Aarr

Barray

Cnums

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined variable names like 'arr' or 'list'.

The input array is named 'nums', so we use nums[mid] to get the middle element.

3fill in blank

hard

Fix the error in the recursive call to build the left subtree.

DSA Javascript

node.left = buildBST(nums, start, [1] - 1);

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Amid

Bstart

Cend

Dmid + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'mid + 1' causes overlap with right subtree.

Using 'end' or 'start' incorrectly limits the range.

We use 'mid - 1' to build the left subtree from start to just before mid.

4fill in blank

hard

Fill both blanks to build the right subtree correctly.

DSA Javascript

node.right = buildBST(nums, [1], [2]);

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Amid + 1

Bmid - 1

Cend

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using mid - 1 as start index for right subtree.

Using start as end index causes wrong range.

Right subtree starts from mid + 1 to end of the array segment.

5fill in blank

hard

Fill all three blanks to complete the main function that calls the helper.

DSA Javascript

function sortedArrayToBST([1]) {
  function buildBST([2], start, end) {
    if (start > end) return null;
    const mid = Math.floor((start + end) / 2);
    const node = new TreeNode(nums[mid]);
    node.left = buildBST(nums, start, mid - 1);
    node.right = buildBST(nums, mid + 1, end);
    return node;
  }
  return buildBST([3], 0, nums.length - 1);
}

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Anums

Darray

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names like 'array' causes reference errors.

The array parameter and recursive calls use the name 'nums' consistently.