[Solved] The following Python code counts set bits for all numbers fr... What is the main inefficiency in this approach?def countBits(n): res = [] for i in range(n+1): res.append(bin(i).count('1')) return res | Bit Manipulation

Bit Manipulation - Counting Bits (0 to N)

The following Python code counts set bits for all numbers from 0 to n by converting each number to a binary string and counting '1's. What is the main inefficiency in this approach?

def countBits(n):
    res = []
    for i in range(n+1):
        res.append(bin(i).count('1'))
    return res

ACounting '1's in string is incorrect for negative numbers

BConverting each number to binary string repeatedly causes high overhead

CThe loop should start from 1, not 0

DThe function does not handle large n due to recursion depth

Step-by-Step Solution

Solution:

Step 1: Analyze the code
Each number i is converted to a binary string using bin(i), then '1's are counted.
Step 2: Identify inefficiency
Converting integers to strings repeatedly is costly in time and memory compared to bitwise operations.
Step 3: Consider alternatives
Bit manipulation or dynamic programming approaches avoid string conversion and are more efficient.
Final Answer:
Option B -> Option B
Quick Check:
String conversion inside loop is expensive [OK]

Quick Trick: Avoid string conversions inside loops for bit counting [OK]

Common Mistakes:

MISTAKES

Thinking counting '1's in string is incorrect for positive numbers
Assuming loop start index affects correctness
Confusing recursion with iteration in this code

Trap Explanation:

PITFALL

String conversion is correct but inefficient, distracts from performance issue

Interviewer Note:

CONTEXT

Tests ability to identify inefficiencies in naive bit counting implementations

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More Bit Manipulation Quizzes

The following Python code counts set bits for all numbers from 0 to n by converting each number to a binary string and counting '1's. What is the main inefficiency in this approach?

Step 1: Analyze the code

Step 2: Identify inefficiency

Step 3: Consider alternatives

Final Answer:

Quick Check:

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