[Solved] Given the following partial state of the continuation byte counter after processing the first 4 bytes:... What was the likely original input sequence leading to this state? | Bit Manipulation

Bit Manipulation - UTF-8 Validation

Given the following partial state of the continuation byte counter after processing the first 4 bytes: remaining = 2, and the next byte is 145 (0b10010001). What was the likely original input sequence leading to this state?

A[240, 162, 138, 147, 145]

B[197, 130, 1, 145, 130]

C[228, 189, 160, 145, 130]

D[235, 140, 4, 145, 130]

Step-by-Step Solution

Solution:

Step 1: Interpret remaining = 2
Means a leading byte requiring 3 bytes total was seen, 2 continuation bytes remain.
Step 2: Check which input starts with 3-byte character
228 (0b11100100) indicates 3-byte character, followed by continuation bytes 189, 160.
Step 3: Next byte 145 (0b10010001) is a valid continuation byte
Matches continuation byte pattern, consistent with [228, 189, 160, 145, 130].
Final Answer:
Option C -> Option C
Quick Check:
Only [228, 189, 160, 145, 130] matches continuation byte count and pattern [OK]

Quick Trick: Remaining count indicates expected continuation bytes [OK]

Common Mistakes:

MISTAKES

Ignoring continuation byte count
Misreading leading bits

Trap Explanation:

PITFALL

Candidates often fail to reverse engineer input from continuation count and byte patterns.

Interviewer Note:

CONTEXT

Tests deep understanding of state tracking in UTF-8 validation.

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More Bit Manipulation Quizzes

What was the likely original input sequence leading to this state?

Step 1: Interpret remaining = 2

Step 2: Check which input starts with 3-byte character

Step 3: Next byte 145 (0b10010001) is a valid continuation byte

Final Answer:

Quick Check:

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