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Examine the following buggy code snippet for the minimum cost tickets problem. Which line contains the subtle bug that can cause incorrect results on some inputs?

medium🐞 Bug Identification Q14 of Q15

Dynamic Programming: Knapsack - Minimum Cost for Tickets

Examine the following buggy code snippet for the minimum cost tickets problem. Which line contains the subtle bug that can cause incorrect results on some inputs?

ALine with dp initialization: dp = [0] * (n + 1)

BLine updating dp[i] = ans after inner loop

CLine setting ans = float('inf') inside outer loop

DLine with bisect.bisect_left call searching from 0 instead of i

Step-by-Step Solution

Step 1: Identify bisect usage
Binary search must start from current index i to avoid counting days before i. Searching from 0 can cause next_i to point to an earlier day, leading to incorrect dp indexing.
Step 2: Confirm other lines are correct
dp initialization, ans reset, and dp assignment are standard and correct. The bug is only in bisect call range.
Final Answer:
Option D -> Option D
Quick Check:
Correct bisect range is [i, n), not [0, n) [OK]

Quick Trick: Check bisect search range carefully [OK]

Common Mistakes:

MISTAKES

Using full array in bisect causing wrong next_i
Forgetting to reset ans
Incorrect dp array size

Trap Explanation:

PITFALL

Searching from 0 looks harmless but breaks monotonicity of dp indices.

Interviewer Note:

CONTEXT

Tests candidate's attention to detail in binary search boundaries within DP.

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