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

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Unformatted text preview: CSE 421 Algorithms Richard Anderson Lecture 8 Optimal Caching Dijkstras algorithm Todays Lecture Optimal Caching (Section 4.3) Dijkstras 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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