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Lecture08 - CSE 421 Algorithms Richard Anderson Lecture 8...

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Unformatted text preview: CSE 421 Algorithms Richard Anderson Lecture 8 Optimal Caching Dijkstra’s algorithm Today’s Lecture • Optimal Caching (Section 4.3) • Dijkstra’s Algorithm (Section 4.4) Optimal Caching • Caching problem: – Maintain collection of items in local memory – Minimize number of items fetched Caching example A, B, C, D, A, E, B, A, D, A, C, B, D, A Optimal Caching • If you know the sequence of requests, what is the optimal replacement pattern? • Note – it is rare to know what the requests are in advance – but we still might want to do this: – Some specific applications, the sequence is known – Competitive analysis, compare performance on an online algorithm with an optimal offline algorithm Farthest in the future algorithm • Discard element used farthest in the future A, B, C, A, C, D, C, B, C, A, D Correctness Proof • Sketch • Start with Optimal Solution O • Convert to Farthest in the Future Solution F-F • Look at the first place where they differ • Convert O to evict F-F element – There are some technicalities here to ensure the caches have the same configuration . . . Single Source Shortest Path...
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Lecture08 - CSE 421 Algorithms Richard Anderson Lecture 8...

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