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Commit 6af84eb

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Dijkstra algorithm
1 parent f1d3085 commit 6af84eb

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6 files changed

+204
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‎src/main/kotlin/pl/dmichalski/algorithms/data_structures/_11_graph_traversal/Runner.kt‎

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@@ -32,8 +32,6 @@ object Runner {
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val breadthFirstSearch = undirectedGraph.breadthFirstSearch(VERTEX_A)
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println("Graph elements: $breadthFirstSearch")
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printUndirectedGraph(undirectedGraph)
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}
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/**
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package pl.dmichalski.algorithms.data_structures._12_dijkstra_algorithm
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class Connection(private val vertex: String, private val weight: Int) {
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fun getVertex(): String {
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return vertex
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}
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fun getWeight(): Int {
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return weight
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}
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override fun toString(): String {
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return "Connection(vertex='$vertex', weight=$weight)"
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}
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}
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package pl.dmichalski.algorithms.data_structures._12_dijkstra_algorithm
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data class Node(private val vertex: String, private val connections: MutableList<Connection>) {
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fun getVertex(): String {
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return vertex
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}
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fun getConnections(): MutableList<Connection> {
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return connections
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}
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override fun toString(): String {
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return "Node(vertex='$vertex', connections=$connections)"
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}
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}
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package pl.dmichalski.algorithms.data_structures._12_dijkstra_algorithm
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class QueueNode(private val value: String, private val priority: Int) {
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fun getValue(): String {
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return value
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}
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fun getPriority(): Int {
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return priority
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}
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}
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package pl.dmichalski.algorithms.data_structures._12_dijkstra_algorithm
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object Runner {
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private const val VERTEX_A = "A"
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private const val VERTEX_B = "B"
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private const val VERTEX_C = "C"
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private const val VERTEX_D = "D"
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private const val VERTEX_E = "E"
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private const val VERTEX_F = "F"
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@JvmStatic
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fun main(args: Array<String>) {
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println("------------------ Initial weighted graph ------------------ ")
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var weightedGraph = getWeightedGraph()
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printWeightedGraph(weightedGraph)
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println("------------------ Finding the shortest path using Dijkstra algorithm ------------------ ")
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weightedGraph = getWeightedGraph()
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val shortestPath = weightedGraph.dijkstra(VERTEX_A, VERTEX_E)
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println("Shortest path between $VERTEX_A and $VERTEX_E: $shortestPath")
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}
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/**
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* It returns weighted graph like this:
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* <pre>
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* 4
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* A --------- B
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* 2 / |
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* / 2 |
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* C ------- D | 3
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* \ / \ |
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* 4 \ 1 / \ 3 |
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* \ / \ |
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* F --------- E
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* 1
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*
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* </pre>
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*/
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private fun getWeightedGraph(): WeightedGraph {
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val weightedGraph = WeightedGraph()
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weightedGraph.addVertex(VERTEX_A)
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weightedGraph.addVertex(VERTEX_B)
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weightedGraph.addVertex(VERTEX_C)
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weightedGraph.addVertex(VERTEX_D)
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weightedGraph.addVertex(VERTEX_E)
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weightedGraph.addVertex(VERTEX_F)
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weightedGraph.addEdge(VERTEX_A, VERTEX_B, 4)
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weightedGraph.addEdge(VERTEX_A, VERTEX_C, 2)
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weightedGraph.addEdge(VERTEX_B, VERTEX_E, 3)
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weightedGraph.addEdge(VERTEX_C, VERTEX_D, 2)
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weightedGraph.addEdge(VERTEX_C, VERTEX_F, 4)
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weightedGraph.addEdge(VERTEX_D, VERTEX_E, 3)
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weightedGraph.addEdge(VERTEX_D, VERTEX_F, 1)
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weightedGraph.addEdge(VERTEX_E, VERTEX_F, 1)
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return weightedGraph
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}
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private fun printWeightedGraph(weightedGraph: WeightedGraph) {
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println(weightedGraph)
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}
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}
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package pl.dmichalski.algorithms.data_structures._12_dijkstra_algorithm
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import java.util.*
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import kotlin.collections.ArrayList
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import kotlin.collections.HashMap
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class WeightedGraph {
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private val adjacencyList: MutableList<Node> = ArrayList()
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fun addVertex(vertex: String) {
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val node = findNode(vertex)
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if (node == null) {
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val newNode = Node(vertex, mutableListOf())
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this.adjacencyList.add(newNode)
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}
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}
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fun addEdge(vertex1: String, vertex2: String, weight: Int) {
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val node1 = findNode(vertex1)
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val node2 = findNode(vertex2)
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val connection1 = Connection(vertex1, weight)
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val connection2 = Connection(vertex2, weight)
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node1!!.getConnections().add(connection2)
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node2!!.getConnections().add(connection1)
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}
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fun dijkstra(start: String, finish: String): List<String> {
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val compareByWeight: Comparator<QueueNode> = compareBy { it.getPriority() }
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val nodesQueue = PriorityQueue(compareByWeight)
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val path: MutableList<String> = ArrayList()
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val distances = HashMap<String, Int>(adjacencyList.size)
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val previous = HashMap<String, String?>(adjacencyList.size)
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var smallest: String
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for (vertexNode in adjacencyList) {
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val vertex = vertexNode.getVertex()
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if (vertex == start) {
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distances[vertex] = 0
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val queueNode = QueueNode(vertex, 0)
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nodesQueue.add(queueNode)
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} else {
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distances[vertex] = Int.MAX_VALUE
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val queueNode = QueueNode(vertex, Int.MAX_VALUE)
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nodesQueue.add(queueNode)
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}
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previous[vertex] = null
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}
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while (nodesQueue.size > 0) {
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smallest = nodesQueue.poll().getValue()
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if (smallest === finish) {
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while (previous[smallest] != null) {
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path.add(smallest)
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smallest = previous[smallest]!!
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}
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break
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}
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if (distances[smallest] != Int.MAX_VALUE) {
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val node = adjacencyList.first { vertexNode -> vertexNode.getVertex() === smallest }
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for (neighbor in node.getConnections()) {
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val candidate = distances[smallest]?.plus(neighbor.getWeight())
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val nextNeighbor = neighbor.getVertex()
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if (candidate!! < distances[nextNeighbor]!!) {
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distances[nextNeighbor] = candidate
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previous[nextNeighbor] = smallest
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val queueNode = QueueNode(nextNeighbor, candidate)
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nodesQueue.add(queueNode)
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}
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}
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}
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}
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return path
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}
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override fun toString(): String {
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return "UndirectedGraph(adjacencyList='$adjacencyList')\n"
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}
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private fun findNode(vertex: String): Node? {
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return adjacencyList.stream()
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.filter { node -> node.getVertex() == vertex }
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.findFirst()
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.orElse(null)
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}
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}

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