Given the following code snippet implementing the min-heap approach for minimum platforms, what is the output for arrivals = [900, 940, 950, 1100, 1500, 1800] and departures = [910, 1200, 1120, 1130, 1900, 2000]?

easy🧾 Code Trace Q3 of Q15

Greedy Algorithms - Minimum Platforms (Train Stations)

Step-by-Step Solution

Solution:

Step 1: Trace heap operations for each train
Trains sorted by arrival: (900,910), (940,1200), (950,1120), (1100,1130), (1500,1900), (1800,2000). At 900, heap=[910]. At 940, heap=[910,1200]. At 950, heap=[910,1120,1200]. At 1100, pop 910 (<=1100), heap=[1120,1200], push 1130 -> heap size 3. Max platforms = 3.
Step 2: Confirm max heap size is 3
Later arrivals reduce heap size, max remains 3.
Final Answer:
Option A -> Option A
Quick Check:
Heap size peaks at 3 platforms [OK]

Quick Trick: Heap size tracks active trains -> max platforms [OK]

Common Mistakes:

MISTAKES

Forgetting to pop from heap when train departs
Miscounting max heap size
Mixing arrival and departure times

Trap Explanation:

PITFALL

Candidates often forget to pop all trains that have departed before current arrival, inflating platform count.

Interviewer Note:

CONTEXT

Tests ability to mentally execute heap-based greedy code.

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More Greedy Algorithms Quizzes

Given the following code snippet implementing the min-heap approach for minimum platforms, what is the output for arrivals = [900, 940, 950, 1100, 1500, 1800] and departures = [910, 1200, 1120, 1130, 1900, 2000]?

Step 1: Trace heap operations for each train

Step 2: Confirm max heap size is 3

Final Answer:

Quick Check:

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