88 lines
2.8 KiB
Kotlin
88 lines
2.8 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.graph.DirectedGraph
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import it.norangeb.algorithms.graph.UndirectedGraph
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import java.util.Stack
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class DirectedCycle(graph: DirectedGraph) {
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var cycle: MutableCollection<Int>? = null
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private val graphInfo = Array(graph.vertexNumber()) { VertexInfo() }
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init {
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(0 until graph.vertexNumber())
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.forEach {
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if (!graphInfo[it].visited)
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dfs(graph, it)
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}
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}
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fun hasCycle(): Boolean = cycle != null
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private fun dfs(graph: UndirectedGraph, vertex: Int) {
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graphInfo[vertex].visited = true
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graphInfo[vertex].onStack = true
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graph.adjacentVertex(vertex)
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.forEach {
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when {
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hasCycle() -> return@forEach
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!graphInfo[it].visited -> exploreChild(graph, vertex, it)
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graphInfo[it].onStack -> cycle = makeCycle(vertex, it)
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}
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}
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graphInfo[vertex].onStack = false
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}
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private fun makeCycle(start: Int, end: Int): MutableCollection<Int> {
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val cycle = Stack<Int>()
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var currentVertex = start
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while (currentVertex != end) {
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cycle.add(currentVertex)
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currentVertex = graphInfo[currentVertex].previously
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}
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cycle.add(end)
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cycle.add(start)
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return cycle
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}
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private fun exploreChild(graph: UndirectedGraph, parent: Int, child: Int) {
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graphInfo[child].previously = parent
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dfs(graph, child)
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}
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data class VertexInfo(
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var visited: Boolean = false,
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var onStack: Boolean = false,
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var previously: Int = -1
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)
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} |