Two Sum in BST in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the BST node is null.

DSA Typescript

if (root [1] null) return false;

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A===

B!==

C>=

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' or '!==' instead of '===' causes wrong base case.

Using comparison operators like '>=' with null is incorrect.

We check if root is exactly equal to null to stop recursion.

2fill in blank

medium

Complete the code to add a value to the set.

DSA Typescript

seenValues.[1](root.val);

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Aappend

Badd

Cpush

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'push' causes runtime error because Set has no push method.

Using 'append' or 'insert' are not valid Set methods.

Sets use 'add' method to insert new elements.

3fill in blank

hard

Fix the error in checking if the complement exists in the set.

DSA Typescript

if (seenValues.[1](target - root.val)) return true;

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Aincludes

Bcontains

Chas

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'contains' or 'includes' causes errors because Set does not have these methods.

Using 'find' returns element or undefined, not boolean.

'has' is the correct method to check presence in a Set.

4fill in blank

hard

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

DSA Typescript

return dfs(root.[1], target, seenValues) || dfs(root.[2], target, seenValues);

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Aleft

Bright

Cparent

Dchild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'parent' causes undefined errors.

Using 'child' is not a valid property.

We recursively search left and right children of the current node.

5fill in blank

hard

Fill all three blanks to complete the main function that starts DFS with an empty set.

DSA Typescript

function findTarget(root: TreeNode | null, target: number): boolean {
  const seenValues = new Set<number>();
  return dfs([1], [2], [3]);
}

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

Aroot

Btarget

CseenValues

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Passing 'null' instead of root causes immediate false return.

Passing wrong order of arguments causes runtime errors.

We start DFS with root node, target number, and empty set.