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Consider the following Python code implementing the optimal car pooling solution. What is the return value when called with trips = [[2,1,5],[3,3,7]] and capacity = 4?

easy🧾 Code Trace Q12 of Q15
Intervals - Car Pooling
Consider the following Python code implementing the optimal car pooling solution. What is the return value when called with trips = [[2,1,5],[3,3,7]] and capacity = 4?
def carPooling(trips, capacity):
    max_location = 0
    for _, start, end in trips:
        max_location = max(max_location, end)
    diff = [0] * (max_location + 1)
    for num, start, end in trips:
        diff[start] += num
        diff[end] -= num
    current_passengers = 0
    for i in range(max_location + 1):
        current_passengers += diff[i]
        if current_passengers > capacity:
            return false
    return true

print(carPooling([[2,1,5],[3,3,7]], 4))
AError due to index out of range
Btrue
Cfalse
Dtrue only if capacity is at least 5
Step-by-Step Solution
Solution:
  1. Step 1: Build difference array

    diff after processing trips: diff[1]+=2, diff[5]-=2, diff[3]+=3, diff[7]-=3
  2. Step 2: Sweep through diff to track passengers

    At location 1: current_passengers=2; at 3: current_passengers=5 (2+3), which exceeds capacity=4 -> return false
  3. Final Answer:

    Option C -> Option C
  4. Quick Check:

    Passenger count exceeds capacity at location 3 [OK]
Quick Trick: Sum diffs to track passengers, check capacity [OK]
Common Mistakes:
MISTAKES
  • Off-by-one in diff array indexing
  • Checking capacity only at trip start
  • Forgetting to decrement at trip end
Trap Explanation:
PITFALL
  • Candidates often miss that passengers accumulate at start before decrement at end, causing off-by-one errors.
Interviewer Note:
CONTEXT
  • Tests ability to mentally execute sweep line code and track state precisely.
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