BST Find Maximum Element in DSA Javascript - 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 to the right child until no right child exists; that node is the maximum.

Execution Sample

DSA Javascript

function findMax(root) {
  let current = root;
  while (current.right !== null) {
    current = current.right;
  }
  return current.value;
}

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 right	20	Yes	current = current.right (20)	15 / \ 10 20 / \ 17 25
3	Move right	25	No	current = current.right (25)	15 / \ 10 20 / \ 17 25
4	No right child	25	No	Stop	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	Final
current.value	15	15	20	25	25

Key Moments - 3 Insights

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

In a BST, all right children have values greater than their parent. The execution_table rows 1 to 3 show moving right to find larger values until no right child exists.

What if the tree has only one node?

If the root has no right child (like step 1 with no right child), the root itself is the maximum, as shown in the exit condition at step 4.

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

Stopping when current.right is null means current is the largest node. If we moved until current is null, we would go past the largest node, losing the reference. See step 4 in execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of current after step 2?

A 20

B 15

C 25

D 17

💡 Hint

Check the 'Current Node Value' column at step 2 in execution_table.

At which step does the algorithm stop because there is no right child?

A Step 3

B Step 2

C Step 4

D Step 1

💡 Hint

Look for the step where 'Right Child Exists?' is 'No' and operation is 'No right child' in execution_table.

If the node with value 25 had a right child 30, what would be the current node value after step 3?

A 25

B 30

C 20

D 17

💡 Hint

If right child exists, current moves right as per execution_table steps 2 and 3.

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 right subtree has larger values

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. Repeat this until the current node has no right child. The node without a right child is the maximum element. This works because in BSTs, right children always have greater values than their parents. The code uses a loop to move right until no right child is found, then returns that node's value.