BST Find Maximum Element in DSA Typescript - Execution Trace

Concept Flow - BST Find Maximum Element

Start at root node

↓

Check if right child exists?

No→Current node is max

Yes↓

Move to right child

↩Back to check right child

Start at the root and keep moving right until no right child exists; that node is the maximum.

Execution Sample

DSA Typescript

function findMax(root: TreeNode | null): number | null {
  if (!root) return null;
  let current = root;
  while (current.right) {
    current = current.right;
  }
  return current.val;
}

This code finds the maximum value in a BST by moving right until no right child exists.

Execution Table

Step	Operation	Current Node Value	Right Child Exists?	Pointer Changes	Visual State
1	Start at root	15	Yes	current = root (15)	15 / \ 10 20 / \ 17 25
2	Move to right child	20	Yes	current = current.right (20)	15 / \ 10 20 / \ 17 25
3	Move to right child	25	No	current = current.right (25)	15 / \ 10 20 / \ 17 25
4	Check right child	25	No	current stays at 25	15 / \ 10 20 / \ 17 25
5	Return max value	25	N/A	Return 25	15 / \ 10 20 / \ 17 25

💡 No right child at node 25, so 25 is the maximum element.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
current.val	N/A	15	20	25	25	25
current.right	N/A	Node(20)	Node(25)	null	null	null

Key Moments - 3 Insights

Why do we keep moving to the right child to find the maximum?

Because in a BST, all right children have values greater than their parent. The execution_table rows 1 to 4 show moving right until no right child exists.

What if the tree is empty (root is null)?

The code returns null immediately (see execution_sample line 2). No steps occur in execution_table because the tree is empty.

Why do we stop when current.right is null, not when current is null?

Because current is always a valid node. We stop when there is no right child to move to, meaning current is the max. See execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'current.val' at Step 3?

A 25

B 15

C 20

D 17

💡 Hint

Check the 'Current Node Value' column at Step 3 in execution_table.

At which step does the condition 'Right Child Exists?' become No?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Right Child Exists?' column in execution_table.

If the root had no right child, how would the execution_table change?

A It would move to Step 2 and beyond

B It would return null immediately

C It would stop at Step 1 with 'Right Child Exists?' as No

D It would cause an error

💡 Hint

Refer to the flow where right child check is done; if none exists at root, we stop immediately.

Concept Snapshot

BST Find Maximum Element:
- Start at root node
- While right child exists, move right
- When no right child, current node is max
- Return current node's value
- Works because BST right children are larger

Full Transcript

To find the maximum element in a Binary Search Tree (BST), start at the root node. Check if the current node has a right child. If yes, move to that right child and repeat. Continue moving right until you reach a node with no right child. That node contains the maximum value in the BST. If the tree is empty, return null. This works because in BSTs, right children always have greater values than their parents. The code sample shows this logic using a while loop. The execution table traces each step, showing the current node and pointer changes until the maximum is found.