BST Inorder Successor in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the left child of a node.

DSA Typescript

function getLeftChild(node: TreeNode | null): TreeNode | null {
  return node[1];
}

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

A.left

B.right

C.parent

D.value

Attempts:

3 left

💡 Hint

Common Mistakes

Using .right instead of .left

Using .parent or .value which are not children

The left child of a node in a BST is accessed using the .left property.

2fill in blank

medium

Complete the code to find the minimum node in a BST subtree.

DSA Typescript

function findMin(node: TreeNode | null): TreeNode | null {
  while (node && node[1]) {
    node = node.left;
  }
  return node;
}

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

A.value

B.right

C.parent

D.left

Attempts:

3 left

💡 Hint

Common Mistakes

Checking node.right instead of node.left

Returning node without checking children

To find the minimum node, keep going left until no left child exists.

3fill in blank

hard

Fix the error in the code to correctly find the inorder successor when the node has no right child.

DSA Typescript

function inorderSuccessor(root: TreeNode | null, p: TreeNode): TreeNode | null {
  let successor: TreeNode | null = null;
  while (root) {
    if (p.value < root.value) {
      successor = root;
      root = root[1];
    } else {
      root = root.right;
    }
  }
  return successor;
}

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

A.right

B.left

C.parent

D.value

Attempts:

3 left

💡 Hint

Common Mistakes

Moving right instead of left when p.value < root.value

Using root.parent which is not available

When p.value is less than root.value, move to root.left to find a smaller candidate successor.

4fill in blank

hard

Fill both blanks to complete the function that finds the inorder successor of a node in a BST.

DSA Typescript

function inorderSuccessor(root: TreeNode | null, p: TreeNode): TreeNode | null {
  if (p.right) {
    return findMin(p[1]);
  }
  let successor: TreeNode | null = null;
  while (root) {
    if (p.value < root.value) {
      successor = root;
      root = root[2];
    } else {
      root = root.right;
    }
  }
  return successor;
}

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

A.left

B.right

C.parent

D.value

Attempts:

3 left

💡 Hint

Common Mistakes

Using p.left instead of p.right for right subtree

Moving root.right instead of root.left in the loop

If p has a right child, successor is the minimum in right subtree (p.right). Otherwise, move left in root to find successor.

5fill in blank

hard

Fill all three blanks to complete the helper function and the inorder successor logic.

DSA Typescript

function findMin(node: TreeNode | null): TreeNode | null {
  while (node && node[1]) {
    node = node[2];
  }
  return node;
}

function inorderSuccessor(root: TreeNode | null, p: TreeNode): TreeNode | null {
  if (p.right) {
    return findMin(p[3]);
  }
  let successor: TreeNode | null = null;
  while (root) {
    if (p.value < root.value) {
      successor = root;
      root = root.left;
    } else {
      root = root.right;
    }
  }
  return successor;
}

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

A.left

B.right

C.parent

D.value

Attempts:

3 left

💡 Hint

Common Mistakes

Using node.right instead of node.left in findMin

Using p.left instead of p.right for successor

To find minimum, keep moving left while node.left exists. For successor, if p has right child, find minimum in p.right subtree.