[Solved] Given the following code snippet for serialization using BFS, what is... Given the following code snippet for serialization using BFS, what is the serialized string output for the binary tree below? | Tree: Depth-First Search

Tree: Depth-First Search - Serialize and Deserialize Binary Tree

Given the following code snippet for serialization using BFS, what is the serialized string output for the binary tree below? Tree: 1 / \ 2 3 / \ 4 null

from collections import deque

def serialize(root):
    if not root:
        return ''
    queue = deque([root])
    vals = []
    while queue:
        node = queue.popleft()
        if node:
            vals.append(str(node.val))
            queue.append(node.left)
            queue.append(node.right)
        else:
            vals.append('X')
    while vals and vals[-1] == 'X':
        vals.pop()
    return ','.join(vals)

A1,2,3,4,X,X,X

B1,2,3,X,X,4

C1,2,3,X,X,4,X,X,X

D1,2,3,X,X,4,X

Step-by-Step Solution

Step 1: Trace queue processing
Start with queue=[1]. Pop 1, append '1', enqueue 2 and 3. Queue=[2,3].
Step 2: Continue BFS and record values
Pop 2, append '2', enqueue left and right (both null) -> enqueue X,X. Pop 3, append '3', enqueue 4 and null -> enqueue 4,X. Pop nulls append 'X'. Remove trailing 'X's at end.
Final Answer:
Option B -> Option B
Quick Check:
Serialized string matches BFS with null markers trimmed correctly [OK]

Quick Trick: Trailing 'X's are removed after BFS serialization [OK]

Common Mistakes:

MISTAKES

Including trailing null markers that should be trimmed
Missing null markers for missing children
Confusing order of nodes in BFS

Trap Explanation:

PITFALL

Candidates often forget to trim trailing 'X's or miscount null children in BFS order.

Interviewer Note:

CONTEXT

Tests ability to mentally execute BFS serialization and handle null markers correctly.

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More Tree: Depth-First Search Quizzes

Given the following code snippet for serialization using BFS, what is the serialized string output for the binary tree below? Tree: 1 / \ 2 3 / \ 4 null

Step 1: Trace queue processing

Step 2: Continue BFS and record values

Final Answer:

Quick Check:

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