79 lines
2.7 KiB
Kotlin
79 lines
2.7 KiB
Kotlin
/*
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* MIT License
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*
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* Copyright (c) 2019 norangebit
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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*/
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package it.norangeb.algorithms.graph.operations
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import it.norangeb.algorithms.datastructures.queue.priority.BinaryHeap
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import it.norangeb.algorithms.datastructures.queue.priority.PriorityQueue
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import it.norangeb.algorithms.graph.WeightUndirectedGraph
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import it.norangeb.algorithms.graph.data.EdgeI
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class Prim(graph: WeightUndirectedGraph) : MinimumSpanningTree {
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private val mst = mutableListOf<EdgeI>()
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private val visited = Array(graph.vertexNumber()) { false }
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init {
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val queue = BinaryHeap.createMinPriorityQueue<EdgeI>()
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visitAdjacent(graph, 0, queue)
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while (!queue.isEmpty() && mst.size < graph.vertexNumber() - 1)
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tryEdge(graph, queue)
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}
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private fun tryEdge(graph: WeightUndirectedGraph, heap: PriorityQueue<EdgeI>) {
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heap.pop().map {
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val from = it.either()
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val to = it.other(from)
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if (visited[from] && visited[to])
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return@map
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if (!visited[from])
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visitAdjacent(graph, from, heap)
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if (!visited[to])
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visitAdjacent(graph, to, heap)
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mst.add(it)
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}
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}
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private fun visitAdjacent(
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graph: WeightUndirectedGraph,
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vertex: Int,
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heap: PriorityQueue<EdgeI>
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) {
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visited[vertex] = true
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graph.adjacentVertex(vertex)
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.forEach {
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if (!visited[it.other(vertex)])
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heap.insert(it)
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}
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}
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override fun edges(): Collection<EdgeI> = mst
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override fun weight(): Double = mst.map { it.weight() }.sum()
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} |