[Solved] Given the following code snippet for minimum cost tickets, which line causes incorrect results due to improper index handling when calculating dp values?for i in range(len(days)-1, -1, -1):... | Dynamic Programming: Knapsack

Dynamic Programming: Knapsack - Minimum Cost for Tickets

Given the following code snippet for minimum cost tickets, which line causes incorrect results due to improper index handling when calculating dp values?

for i in range(len(days)-1, -1, -1):
    j = i
    while j < len(days) and days[j] < days[i] + durations[k]:
        j += 1
    dp[i] = min(dp[i], costs[k] + dp[j])

ALine with while loop condition

BLine updating dp[i] with dp[j]

CLine incrementing j inside while loop

DLine initializing j = i

Step-by-Step Solution

Solution:

Step 1: Analyze dp update line
The line dp[i] = min(dp[i], costs[k] + dp[j]) assumes dp[j] is valid.
Step 2: Check boundary conditions for dp array
If j equals len(days), dp[j] is out of bounds, causing incorrect results or runtime error.
Step 3: Correct approach to handle boundary
Should handle case when j == len(days) by using dp array size + 1 or a sentinel value.
Final Answer:
Option B -> Option B
Quick Check:
Accessing dp[j] without boundary check causes errors [OK]

Quick Trick: Check array bounds when accessing dp[j] [OK]

Common Mistakes:

MISTAKES

Ignoring dp array boundary when j == len(days)
Assuming while loop condition prevents out-of-bounds
Misplacing j initialization

Trap Explanation:

PITFALL

Line looks correct but misses boundary check for dp array

Interviewer Note:

CONTEXT

Tests ability to identify subtle off-by-one errors in DP code

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More Dynamic Programming: Knapsack Quizzes

Given the following code snippet for minimum cost tickets, which line causes incorrect results due to improper index handling when calculating dp values?

Step 1: Analyze dp update line

Step 2: Check boundary conditions for dp array

Step 3: Correct approach to handle boundary

Final Answer:

Quick Check:

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