Two Sum in BST in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Go

if root [1] nil {
    return false
}

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A!=

B<

C==

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' causes the logic to be reversed.

Using comparison operators like '<' or '>' with nil causes errors.

We check if the root is equal to nil to know if we reached the end of a branch.

2fill in blank

medium

Complete the code to insert a value into the map to track visited numbers.

DSA Go

visited[[1]] = true

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Asum

Btarget

Ccomplement

Droot.Val

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'target' or 'sum' instead of the node's value.

Using 'complement' which is the needed pair value, not the current node.

We mark the current node's value as visited by setting visited[root.Val] = true.

3fill in blank

hard

Fix the error in the condition to check if the complement exists in the map.

DSA Go

if _, ok := visited[[1]]; ok {
    return true
}

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Atarget - root.Val

Broot.Val - target

Croot.Val + target

Dtarget + root.Val

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of subtraction.

Reversing the subtraction order.

The complement is target minus the current node's value to find the needed pair.

4fill in blank

hard

Fill both blanks to recursively search left and right subtrees.

DSA Go

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

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ALeft

BRight

Cleft

Dright

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase 'Left' or 'Right' causes compilation errors.

Swapping left and right fields.

In Go, struct fields start with lowercase letters for unexported fields, so use 'left' and 'right'.

5fill in blank

hard

Fill all three blanks to complete the TwoSumBST function using DFS and a map.

DSA Go

func TwoSumBST(root *TreeNode, target int) bool {
    visited := make(map[int]bool)
    var dfs func(node *TreeNode, target int, visited map[int]bool) bool
    dfs = func(node *TreeNode, target int, visited map[int]bool) bool {
        if node [1] nil {
            return false
        }
        complement := target [2] node.Val
        if _, ok := visited[complement]; ok {
            return true
        }
        visited[node.Val] = true
        return dfs(node.[3], target, visited) || dfs(node.right, target, visited)
    }
    return dfs(root, target, visited)
}

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

A==

B-

Cleft

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' for nil check.

Adding instead of subtracting for complement.

Using uppercase 'Left' instead of 'left'.

Check if node is nil with '==', find complement by subtracting node.Val from target, and recurse left subtree with 'left'.