19.2 Greedy Algorithms: Tools and Techniques, Schemes and Mind Maps of Design

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Algorithms & Models of Computation

CS/ECE 374, Fall 2020

Greedy Algorithms: Tools and Techniques

FLNAME:19.2.0.0 ZZZ:19.2.0.0 Greedy Algorithms: Tools and Techniques

What is a Greedy Algorithm?

No real consensus on a universal definition.

Greedy algorithms: (^1) make decision incrementally in small steps without backtracking (^2) decision at each step is based on improving local or current state in a myopic fashion without paying attention to the global situation (^3) decisions often based on some fixed and simple priority rules

What is a Greedy Algorithm?

No real consensus on a universal definition.

Greedy algorithms: (^1) make decision incrementally in small steps without backtracking (^2) decision at each step is based on improving local or current state in a myopic fashion without paying attention to the global situation (^3) decisions often based on some fixed and simple priority rules

Pros and Cons of Greedy Algorithms

Pros: (^1) Usually (too) easy to design greedy algorithms (^2) Easy to implement and often run fast since they are simple (^3) Several important cases where they are effective/optimal (^4) Lead to a first-cut heuristic when problem not well understood Cons: (^1) Very often greedy algorithms don’t work. Easy to lull oneself into believing they work (^2) Many greedy algorithms possible for a problem and no structured way to find effective ones CS 374: Every greedy algorithm needs a proof of correctness

Pros and Cons of Greedy Algorithms

Pros: (^1) Usually (too) easy to design greedy algorithms (^2) Easy to implement and often run fast since they are simple (^3) Several important cases where they are effective/optimal (^4) Lead to a first-cut heuristic when problem not well understood Cons: (^1) Very often greedy algorithms don’t work. Easy to lull oneself into believing they work (^2) Many greedy algorithms possible for a problem and no structured way to find effective ones CS 374: Every greedy algorithm needs a proof of correctness

Greedy Algorithm Types

Crude classification: (^1) Non-adaptive: fix some ordering of decisions a priori and stick with the order (^2) Adaptive: make decisions adaptively but greedily/locally at each step

Plan: (^1) See several examples (^2) Pick up some proof techniques

THE END

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