From 7a2c9410249efb879bc37f28eb0b373713be1d1b Mon Sep 17 00:00:00 2001 From: Sampada <46674082+sampada07@users.noreply.github.com> Date: Fri, 6 Mar 2020 21:19:00 +0530 Subject: [PATCH] BAEL-3883: Boruvka's Algorithm for Minimum-Spanning Trees (#8816) * BAEL-3883: Boruvka's Algorithm for Minimum-Spanning Trees * BAEL-3883: checking in pom.xml --- algorithms-miscellaneous-5/pom.xml | 12 ++++ .../algorithms/boruvka/BoruvkaMST.java | 61 +++++++++++++++++ .../algorithms/boruvka/DisjointSet.java | 49 ++++++++++++++ .../com/baeldung/algorithms/boruvka/Edge.java | 40 ++++++++++++ .../baeldung/algorithms/boruvka/Graph.java | 64 ++++++++++++++++++ .../baeldung/algorithms/boruvka/Input.java | 65 +++++++++++++++++++ .../com/baeldung/algorithms/boruvka/Tree.java | 63 ++++++++++++++++++ .../algorithms/boruvka/BoruvkaUnitTest.java | 48 ++++++++++++++ .../src/test/resources/input.json | 41 ++++++++++++ 9 files changed, 443 insertions(+) create mode 100644 algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/BoruvkaMST.java create mode 100644 algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/DisjointSet.java create mode 100644 algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Edge.java create mode 100644 algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Graph.java create mode 100644 algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Input.java create mode 100644 algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Tree.java create mode 100644 algorithms-miscellaneous-5/src/test/java/com/baeldung/algorithms/boruvka/BoruvkaUnitTest.java create mode 100644 algorithms-miscellaneous-5/src/test/resources/input.json diff --git a/algorithms-miscellaneous-5/pom.xml b/algorithms-miscellaneous-5/pom.xml index 4f9cc8b711..2799c39971 100644 --- a/algorithms-miscellaneous-5/pom.xml +++ b/algorithms-miscellaneous-5/pom.xml @@ -39,6 +39,16 @@ guava ${guava.version} + + com.fasterxml.jackson.core + jackson-databind + ${jackson.version} + + + org.junit.platform + junit-platform-commons + ${junit.platform.version} + org.assertj @@ -66,6 +76,8 @@ 1.11 3.6.1 28.1-jre + 2.10.2 + 1.6.0 \ No newline at end of file diff --git a/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/BoruvkaMST.java b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/BoruvkaMST.java new file mode 100644 index 0000000000..0f8bc5b296 --- /dev/null +++ b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/BoruvkaMST.java @@ -0,0 +1,61 @@ +package com.baeldung.algorithms.boruvka; + +public class BoruvkaMST { + + private static Tree mst = new Tree(); + private static int totalWeight; + + public BoruvkaMST(Graph graph) { + DisjointSet dSet = new DisjointSet(graph.getNodes()); + + // repeat at most log N times or until we have N-1 edges + for (int t = 1; t < graph.getNodes() && mst.getEdgeCount() < graph.getNodes() - 1; t = t + t) { + + // foreach tree in forest, find closest edge + Edge[] closestEdgeArray = new Edge[graph.getNodes()]; + for (Edge edge : graph.getAllEdges()) { + int first = edge.getFirst(); + int second = edge.getSecond(); + int firstParent = dSet.getParent(first); + int secondParent = dSet.getParent(second); + if (firstParent == secondParent) { + continue; // same tree + } + if (closestEdgeArray[firstParent] == null || edge.getWeight() < closestEdgeArray[firstParent].getWeight()) { + closestEdgeArray[firstParent] = edge; + } + if (closestEdgeArray[secondParent] == null || edge.getWeight() < closestEdgeArray[secondParent].getWeight()) { + closestEdgeArray[secondParent] = edge; + } + } + + // add newly discovered edges to MST + for (int i = 0; i < graph.getNodes(); i++) { + Edge edge = closestEdgeArray[i]; + if (edge != null) { + int first = edge.getFirst(); + int second = edge.getSecond(); + // don't add the same edge twice + if (dSet.getParent(first) != dSet.getParent(second)) { + mst.addEdge(edge); + totalWeight += edge.getWeight(); + dSet.union(first, second); + } + } + } + } + } + + public Iterable getMST() { + return mst; + } + + public int getTotalWeight() { + return totalWeight; + } + + public String toString() { + return "MST: " + mst.toString() + " | Total Weight: " + totalWeight; + } + +} diff --git a/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/DisjointSet.java b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/DisjointSet.java new file mode 100644 index 0000000000..7769686e36 --- /dev/null +++ b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/DisjointSet.java @@ -0,0 +1,49 @@ +package com.baeldung.algorithms.boruvka; + +import java.util.Arrays; + +public class DisjointSet { + + private int[] nodeParents; + private int[] nodeRanks; + + public DisjointSet(int n) { + nodeParents = new int[n]; + nodeRanks = new int[n]; + for (int i = 0; i < n; i++) { + nodeParents[i] = i; + nodeRanks[i] = 0; + } + } + + public int getParent(int node) { + while (node != nodeParents[node]) { + node = nodeParents[node]; + } + return node; + } + + public void union(int node1, int node2) { + int node1Parent = getParent(node1); + int node2Parent = getParent(node2); + if (node1Parent == node2Parent) { + return; + } + + if (nodeRanks[node1Parent] < nodeRanks[node2Parent]) { + nodeParents[node1Parent] = node2Parent; + } + else if (nodeRanks[node1Parent] > nodeRanks[node2Parent]) { + nodeParents[node2Parent] = node1Parent; + } + else { + nodeParents[node2Parent] = node1Parent; + nodeRanks[node1Parent]++; + } + } + + public String toString() { + return "Parent: " + Arrays.toString(nodeParents) + "Rank: " + Arrays.toString(nodeRanks); + } + +} diff --git a/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Edge.java b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Edge.java new file mode 100644 index 0000000000..6ee136fc48 --- /dev/null +++ b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Edge.java @@ -0,0 +1,40 @@ +package com.baeldung.algorithms.boruvka; + +public class Edge { + + private final int first; + private final int second; + private final int weight; + + public Edge(int first, int second, int weight) { + this.first = first; + this.second = second; + this.weight = weight; + } + + public double getWeight() { + return weight; + } + + public int getFirst() { + return first; + } + + public int getSecond() { + return second; + } + + public int getOtherNode(int firstNode) { + int secondNode = 0; + if (firstNode == first) + secondNode = second; + else if (firstNode == second) + secondNode = first; + return secondNode; + } + + public String toString() { + return String.format("%d-%d %d", first, second, weight); + } + +} diff --git a/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Graph.java b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Graph.java new file mode 100644 index 0000000000..e899007dfa --- /dev/null +++ b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Graph.java @@ -0,0 +1,64 @@ +package com.baeldung.algorithms.boruvka; + +import java.io.IOException; + +import com.fasterxml.jackson.core.JsonParseException; +import com.fasterxml.jackson.databind.JsonMappingException; + +public class Graph { + + private int nodes; + private int edges; + private Tree[] trees; + + public Graph(Input jsonGraph) throws JsonParseException, JsonMappingException, IOException { + nodes = jsonGraph.getNodes(); + trees = (Tree[]) new Tree[nodes]; + for (int i = 0; i < nodes; i++) { + trees[i] = new Tree(); + } + + int edgesFromInput = jsonGraph.getEdges(); + for (int i = 0; i < edgesFromInput; i++) { + int first = jsonGraph.getEdgeList() + .get(i) + .getFirst(); + int second = jsonGraph.getEdgeList() + .get(i) + .getSecond(); + int weight = jsonGraph.getEdgeList() + .get(i) + .getWeight(); + Edge edge = new Edge(first, second, weight); + + trees[first].addEdge(edge); + trees[second].addEdge(edge); + edges++; + } + + } + + public int getNodes() { + return nodes; + } + + public int getEdges() { + return edges; + } + + public Iterable iterableTree(int i) { + return trees[i]; + } + + public Iterable getAllEdges() { + Iterable list = new Tree(); + for (int i = 0; i < nodes; i++) { + for (Edge edge : iterableTree(i)) { + if (edge.getOtherNode(i) > i) { + ((Tree) list).addEdge(edge); + } + } + } + return list; + } +} diff --git a/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Input.java b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Input.java new file mode 100644 index 0000000000..b52720d5e9 --- /dev/null +++ b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Input.java @@ -0,0 +1,65 @@ +package com.baeldung.algorithms.boruvka; + +import java.util.List; + +public class Input { + private int nodes; + private int edges; + private List edgeList; + + public int getNodes() { + return nodes; + } + + public void setNodes(int nodes) { + this.nodes = nodes; + } + + public int getEdges() { + return edges; + } + + public void setEdges(int edges) { + this.edges = edges; + } + + public List getEdgeList() { + return edgeList; + } + + public void setEdgeList(List edgeList) { + this.edgeList = edgeList; + } + + static class E { + private int first; + private int second; + private int weight; + + public int getFirst() { + return first; + } + + public void setFirst(int first) { + this.first = first; + } + + public int getSecond() { + return second; + } + + public void setSecond(int second) { + this.second = second; + } + + public int getWeight() { + return weight; + } + + public void setWeight(int weight) { + this.weight = weight; + } + + } + +} diff --git a/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Tree.java b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Tree.java new file mode 100644 index 0000000000..cc28233e07 --- /dev/null +++ b/algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/boruvka/Tree.java @@ -0,0 +1,63 @@ +package com.baeldung.algorithms.boruvka; + +import java.util.Iterator; + +public class Tree implements Iterable { + private Node root; + private int edgeCount; + + private static class Node { + private Edge edge; + private Node next; + + public String toString() { + String nextStr = next != null ? next.toString() : ""; + return edge.toString() + " | " + nextStr; + } + } + + public Tree() { + root = null; + edgeCount = 0; + } + + public int getEdgeCount() { + return edgeCount; + } + + public void addEdge(Edge edge) { + Node oldRoot = root; + root = new Node(); + root.edge = edge; + root.next = oldRoot; + edgeCount++; + } + + public String toString() { + String rootStr = root != null ? root.toString() : ""; + return "Tree: " + rootStr + "Size: " + edgeCount; + } + + public Iterator iterator() { + return new LinkedIterator(root); + } + + private class LinkedIterator implements Iterator { + private Node current; + + public LinkedIterator(Node root) { + current = root; + } + + public boolean hasNext() { + return current != null; + } + + public Edge next() { + Edge edge = current.edge; + current = current.next; + return edge; + } + } + +} diff --git a/algorithms-miscellaneous-5/src/test/java/com/baeldung/algorithms/boruvka/BoruvkaUnitTest.java b/algorithms-miscellaneous-5/src/test/java/com/baeldung/algorithms/boruvka/BoruvkaUnitTest.java new file mode 100644 index 0000000000..1d03d2d4d9 --- /dev/null +++ b/algorithms-miscellaneous-5/src/test/java/com/baeldung/algorithms/boruvka/BoruvkaUnitTest.java @@ -0,0 +1,48 @@ +package com.baeldung.algorithms.boruvka; + +import static org.junit.jupiter.api.Assertions.assertEquals; + +import java.io.BufferedReader; +import java.io.IOException; +import java.io.InputStreamReader; + +import org.junit.Before; +import org.junit.Test; + +import com.fasterxml.jackson.core.JsonParseException; +import com.fasterxml.jackson.databind.JsonMappingException; +import com.fasterxml.jackson.databind.ObjectMapper; + +public class BoruvkaUnitTest { + + private Input input; + private static String INPUT_JSON = "/input.json"; + + @Before + public void convertInputJsonToObject() throws JsonParseException, JsonMappingException, IOException { + ObjectMapper mapper = new ObjectMapper(); + StringBuilder jsonStr = new StringBuilder(); + try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(BoruvkaMST.class.getResourceAsStream(INPUT_JSON)))) { + String line; + while ((line = bufferedReader.readLine()) != null) { + jsonStr.append(line) + .append("\n"); + } + } + + input = mapper.readValue(jsonStr.toString(), Input.class); + + } + + @Test + public void givenInputGraph_whenBoruvkaPerformed_thenMinimumSpanningTree() throws JsonParseException, JsonMappingException, IOException { + Graph graph = new Graph(input); + BoruvkaMST boruvkaMST = new BoruvkaMST(graph); + + Tree mst = (Tree) boruvkaMST.getMST(); + + assertEquals(30, boruvkaMST.getTotalWeight()); + assertEquals(4, mst.getEdgeCount()); + } + +} diff --git a/algorithms-miscellaneous-5/src/test/resources/input.json b/algorithms-miscellaneous-5/src/test/resources/input.json new file mode 100644 index 0000000000..0151f83618 --- /dev/null +++ b/algorithms-miscellaneous-5/src/test/resources/input.json @@ -0,0 +1,41 @@ +{ + "nodes": 5, + "edges": 7, + "edgeList": [ + { + "first": 0, + "second": 1, + "weight": 8 + }, + { + "first": 0, + "second": 2, + "weight": 5 + }, + { + "first": 1, + "second": 2, + "weight": 9 + }, + { + "first": 1, + "second": 3, + "weight": 11 + }, + { + "first": 2, + "second": 3, + "weight": 15 + }, + { + "first": 2, + "second": 4, + "weight": 10 + }, + { + "first": 3, + "second": 4, + "weight": 7 + } + ] +} \ No newline at end of file