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Cheapest Route Within a Stop Limit
Given one-way routes between cities each with a cost, find the cheapest total cost from a source city to a destination city using at most k intermediate stops.
1. Problem Statement
You are given a 2x3 sliding tile board (6 cells, one of which is blank, represented as 0) in a start arrangement and a target arrangement. Each move slides a tile adjacent to the blank into the blank space. Return the minimum number of moves to reach the target arrangement from the start, or -1 if it cannot be reached.
2. Live Coding Format
Work in the provided coding workspace while explaining your decisions to the live interviewer. Validation may use inline tests, examples, comments, or a verbal walkthrough.
3. Key Focus Areas
- 1Problem clarification and contract
- 2Approach exploration and optimality
- 3Think-aloud communication and pacing
- 4Implementation correctness
- 5Code quality and language fluency
- 6Handwritten tests and dry run
- 7Debugging and self-correction
- 8Complexity analysis
- 9Follow-up performance
4. What Strong Candidates Should Demonstrate
- ✓Clarify board encoding, move rules, and unreachable-case behavior before coding.
- ✓Explain an unbounded DFS baseline and improve to visited-state BFS over the configuration graph.
- ✓Think aloud while implementing careful state encoding and neighbor generation.
- ✓Validate with explicit expected outputs and a top-to-bottom handwritten dry run.
- ✓Analyze time and space complexity and handle a focused follow-up extension.
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Practice this problem in the live coding workspace while the interviewer probes your clarification, implementation, trade-offs, and validation.
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