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Identify problems that can be solved using greedy methods

#1
07-20-2020, 03:31 PM
You see greedy methods pick the local best at each step without regret later on. I recall you asking about this stuff before we chatted. It works when the overall solution builds from those early picks alone. Problems like scheduling meetings fit perfectly here. You choose the one ending soonest then repeat on the rest. I bet you notice how that avoids conflicts fast.

But coin systems with standard denominations also bend to greedy picks. You grab the largest coin first then fill the gap smaller. It solves exact change issues when values align certain ways. I found that out testing small amounts myself. Perhaps network routing uses similar logic for quick paths. You grab the nearest unvisited spot and connect onward. Or maybe tree building for minimal connections relies on it too. You sort edges by weight then add without cycles forming.

Now Huffman coding for data shrinks files by assigning short codes to frequent items. You build the tree bottom up merging smallest frequencies always. I think you get how that cuts bits overall. Also shortest paths in graphs without negative weights follow greedy steps. You relax distances from the current closest node repeatedly. It speeds up searches in maps or links.

Fractional knapsack lets you take parts of items by value density. You sort by ratio then load until full. I see you grasping why it beats full item limits sometimes. But activity selection on timelines avoids overlaps this way. You always pick the earliest finisher next. Perhaps job sequencing with deadlines grabs highest profit first. You check slots backward from due dates.

Or clustering points in space might use greedy merges of closest pairs. You combine until groups reach desired count. I know you wonder about limits though. Greedy fails on some knapsacks with whole items only. You need dynamic approaches then instead. But when matroids structure the choices it succeeds reliably.

You explore more with interval graphs for coloring tasks. Greedy assigns lowest possible color to each vertex in order. It keeps the number small overall. Perhaps matrix chain multiplication orders multiplies by cheapest first. You pick smallest cost pair repeatedly. I recall testing this on small matrices yields good results.

Now minimum bottleneck paths pick the max edge minimized. You use modified greedy to find such routes. It helps in capacity limited systems. Or prim like growth starts from one point and expands. You add the cheapest outgoing edge each time. You see the spanning tree emerge naturally.

But traveling salesman approximations sometimes greedy tour nearest cities. You get decent paths though not always optimal. I think you try small instances to compare. Also set cover approximations pick the set covering most uncovered elements. You repeat until all covered. It gives quick bounds on hard problems.

You handle load balancing by assigning tasks to current lightest machine. Greedy keeps peaks low in practice. Perhaps frequency assignment in radios picks least used channel. You minimize interference step by step. I found such cases in comms setups.

Now graph coloring for maps assigns colors avoiding adjacent same. Greedy uses first available in sequence. It works well for planar cases often. Or task ordering for processors schedules longest remaining first. You balance completion times better.

You notice many optimization spots where substructure allows greedy success. I always check the greedy choice property holds before applying. Perhaps you test on random instances too. It builds intuition quick. But proof via exchange argument confirms when it works. You swap any better solution and match the greedy one.

Or matroid intersection combines two structures for more complex picks. You find max weight common independent sets. I see applications in matching with constraints. Perhaps resource allocation in clouds follows value per unit. You allocate to highest ratio repeatedly.

You cover all these by thinking locally optimal yet globally sound. I enjoy how simple rules solve tangled cases. Now edge cases like negative weights break some greedy paths. You switch methods then. But positive only keeps it valid.

Perhaps string matching or parsing uses greedy reductions. You collapse common patterns first. It speeds compression steps. You try on sample texts to see savings. I bet results surprise with frequency skews.

Or vehicle routing with capacity grabs closest feasible stop. You update loads after each addition. It approximates good tours fast. You compare to exact solvers on tiny maps.

You expand to multi criteria by weighting factors first. Greedy then picks by combined score. I know it approximates Pareto fronts sometimes. But tradeoffs need careful tuning always.

Perhaps clustering with k means starts greedy assignments. You update centers after full pass. It converges quick in practice. You rerun with different starts for stability.

Now facility location picks sites covering most demand. You add the one serving uncovered best. It minimizes total distance roughly. I think you apply to store placements.

You see the pattern across domains from graphs to schedules. Greedy shines with optimal substructure proofs. Perhaps you code simulators to verify on bigger data. It reveals when it holds.

Or bin packing first fit decreasing sorts items largest first. You place each in earliest bin fitting. It bounds waste well. You measure against lower limits.

You tackle more with online versions where decisions stick. Greedy adapts without future knowledge. I found competitive ratios useful here. But offline allows sorting for better bounds.

Perhaps matching in bipartite graphs picks cheapest available edge. You grow the pairing step by step. It solves assignment fast. You check Hall conditions mentally.

Now the flow from one problem to next shows greedy versatility. I always start with simple cases before complex. You build up understanding this way.

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bob
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Identify problems that can be solved using greedy methods - by bob - 07-20-2020, 03:31 PM

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Identify problems that can be solved using greedy methods

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