The following Python function attempts to compute the minimum cost to connect sticks: ```python import heapq def min_cost_buggy(sticks): heapq.heapify(sticks) total = 0 while len(sticks) > 1: first = heapq.heappop(sticks) second = heapq.heappop(sticks) cost = first + second total += cost sticks.append(cost) # Bug here return total ``` What is the subtle bug in this code?

medium🐞 Bug Q7 of Q15

Greedy Algorithms - Minimum Cost to Connect Sticks

AUsing list append instead of heappush causes incorrect heap structure

BNot checking if sticks list is empty before popping

CAdding cost to total before popping sticks

DHeapify should be called inside the loop

Step-by-Step Solution

Solution:

Step 1: Identify heap operations
Heapq requires using heappush to maintain heap property.
Step 2: Bug analysis
Using sticks.append(cost) adds element but does not maintain heap order, causing incorrect pops later.
Step 3: Correct fix
Replace sticks.append(cost) with heapq.heappush(sticks, cost).
Final Answer:
Option A -> Option A
Quick Check:
Always use heappush to maintain heap [OK]

Quick Trick: Use heappush, not append, to maintain heap property [OK]

Common Mistakes:

MISTAKES

Appending instead of heappush breaks heap invariant
Misunderstanding heapq usage
Ignoring heap property maintenance

Trap Explanation:

PITFALL

Appending to list looks correct but breaks heap structure causing wrong results.

Interviewer Note:

CONTEXT

Tests knowledge of heap operations and common pitfalls in Python heapq usage.

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Step 1: Identify heap operations

Step 2: Bug analysis

Step 3: Correct fix

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