init repo
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39
app/build.gradle.kts
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39
app/build.gradle.kts
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/*
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* This file was generated by the Gradle 'init' task.
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*
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* This generated file contains a sample Java application project to get you started.
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* For more details on building Java & JVM projects, please refer to https://docs.gradle.org/8.13/userguide/building_java_projects.html in the Gradle documentation.
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*/
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plugins {
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// Apply the application plugin to add support for building a CLI application in Java.
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application
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}
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repositories {
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// Use Maven Central for resolving dependencies.
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mavenCentral()
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}
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dependencies {
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// Use JUnit Jupiter for testing.
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testImplementation(libs.junit.jupiter)
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testRuntimeOnly("org.junit.platform:junit-platform-launcher")
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// This dependency is used by the application.
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implementation(libs.guava)
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}
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// Apply a specific Java toolchain to ease working on different environments.
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java { toolchain { languageVersion = JavaLanguageVersion.of(21) } }
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application {
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// Define the main class for the application.
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mainClass = "fun.youthlic.Graph"
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}
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tasks.named<Test>("test") {
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// Use JUnit Platform for unit tests.
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useJUnitPlatform()
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}
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324
app/src/main/java/fun/youthlic/Graph.java
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324
app/src/main/java/fun/youthlic/Graph.java
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package fun.youthlic;
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import java.util.ArrayList;
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import java.util.Comparator;
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import java.util.HashMap;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Locale;
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import java.util.Map;
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import java.util.Optional;
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import java.util.PriorityQueue;
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import java.util.Random;
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import java.util.function.Function;
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import java.util.stream.IntStream;
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public class Graph {
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public record EdgeRecord(String node1, String node2, int weight) {
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}
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private static class Node {
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String id;
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Map<Node, Integer> edges;
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Node(final String id) {
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this.id = id;
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this.edges = new HashMap<>();
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}
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void addEdge(final Node target) {
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edges.put(target, edges.getOrDefault(target, 0) + 1);
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}
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List<String> getDOTEdges(final Function<EdgeRecord, String> callback) {
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final var dotEdges = new ArrayList<String>();
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for (final var entry : edges.entrySet()) {
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final Node target = entry.getKey();
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final int weight = entry.getValue();
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dotEdges.add(
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callback.apply(new EdgeRecord(id, target.id, weight)) + ";\n");
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}
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return dotEdges;
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}
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List<String> getDOTEdges() {
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final var dotEdges = new ArrayList<String>();
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for (final var entry : edges.entrySet()) {
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final Node target = entry.getKey();
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final int weight = entry.getValue();
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dotEdges.add(
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String.format("%s -> %s [label=\"%d\"];\n", id, target.id, weight));
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}
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return dotEdges;
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}
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}
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public static void main(final String[] args) {
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final var g = new Graph(
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"To explore strange new worlds, To seek out new life and new civilizations");
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final var words = g.findBridgeWords("team", "so");
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System.out.println(words);
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final var path = g.findShortestPath("the", "shared");
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System.out.println(path);
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System.out.println(
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g.toDOT(r -> String.format(
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"\"%s\" -> \"%s\" [label=\"%d\"%s]",
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r.node1 + (path.contains(r.node1) ? "~" : ""),
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r.node2 + (path.contains(r.node2) ? "~" : ""),
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r.weight,
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(path.contains(r.node1) &&
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path.contains(r.node2) &&
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IntStream.range(0, path.size() - 1).anyMatch(
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i -> path.get(i).equals(r.node1) && path.get(i + 1).equals(r.node2)))
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? ",color=\"red\""
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: "")));
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System.out.println(g.computePageRank("new", 0.85));
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System.out.println(g.randomWalk());
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}
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private final Map<String, Node> nodes;
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private Map<Node, Double> pageRanks;
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public Graph(final String input, final double d) {
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nodes = new HashMap<>();
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parse(input);
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initRageRanks(d);
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}
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public Graph(final String input) {
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nodes = new HashMap<>();
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parse(input);
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initRageRanks(0.85);
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}
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public Optional<List<String>> findBridgeWords(final String word1, final String word2) {
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final Node node1 = nodes.get(word1.toLowerCase(Locale.ENGLISH));
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final Node node2 = nodes.get(word2.toLowerCase(Locale.ENGLISH));
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if (node1 == null || node2 == null) {
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return Optional.empty();
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}
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final var bridgeWords = new ArrayList<String>();
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for (final var node : node1.edges.keySet()) {
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if (node.edges.containsKey(node2)) {
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bridgeWords.add(node.id);
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}
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}
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return Optional.of(bridgeWords);
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}
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public List<String> findShortestPath(final String word1, final String word2) {
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final var startWord = word1.toLowerCase(Locale.ENGLISH);
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final var endWord = word2.toLowerCase(Locale.ENGLISH);
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final var path = new ArrayList<String>();
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if (!nodes.containsKey(startWord) || !nodes.containsKey(endWord)) {
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return path;
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}
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final Node startNode = nodes.get(startWord);
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final Node endNode = nodes.get(endWord);
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if (startNode == endNode) {
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path.add(startNode.id);
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return path;
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}
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final var distances = new HashMap<Node, Integer>();
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final var previousNodes = new HashMap<Node, Node>();
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final var queue = new PriorityQueue<Node>(
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Comparator.comparingInt(node -> distances.getOrDefault(node, Integer.MAX_VALUE)));
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for (final var node : nodes.values()) {
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distances.put(node, Integer.MAX_VALUE);
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}
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distances.put(startNode, 0);
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queue.add(startNode);
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while (!queue.isEmpty()) {
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final Node current = queue.poll();
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for (final var edge : current.edges.entrySet()) {
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final Node neighbor = edge.getKey();
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final int weight = edge.getValue();
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final int newDist = distances.get(current) + weight;
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if (newDist < distances.get(neighbor)) {
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distances.put(neighbor, newDist);
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previousNodes.put(neighbor, current);
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queue.add(neighbor);
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}
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}
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}
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if (distances.get(endNode) == Integer.MAX_VALUE) {
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return path;
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}
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final var reversePath = new LinkedList<String>();
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Node current = endNode;
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while (current != null) {
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reversePath.addFirst(current.id);
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current = previousNodes.get(current);
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}
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return reversePath;
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}
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public double computePageRank(final String nodeId, final double d) {
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final Node node = nodes.get(nodeId);
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if (node == null) {
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return 0.0;
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}
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return pageRanks.getOrDefault(node, 0.0);
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}
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public List<String> randomWalk() {
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final var path = new ArrayList<String>();
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if (nodes.isEmpty()) {
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return path;
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}
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final var random = new Random();
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final var nodeIds = new ArrayList<>(nodes.keySet());
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final String startNodeId = nodeIds.get(random.nextInt(nodeIds.size()));
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path.add(startNodeId);
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final var usedEdges = new HashMap<String, Integer>();
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var currentNode = nodes.get(startNodeId);
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while (true) {
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final var availableEdge = new ArrayList<Map.Entry<Node, Integer>>();
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int totalWeight = 0;
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for (final var entry : currentNode.edges.entrySet()) {
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final String edgeKey = currentNode.id + " -> " + entry.getKey().id;
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if (usedEdges.getOrDefault(edgeKey, 0) < 2) {
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availableEdge.add(entry);
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totalWeight += entry.getValue();
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}
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}
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if (availableEdge.isEmpty()) {
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break;
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}
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final double randomValue = random.nextDouble() * totalWeight;
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double cumulative = 0.0;
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Node nextNode = null;
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for (final var entry : availableEdge) {
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cumulative += entry.getValue();
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if (randomValue < cumulative) {
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nextNode = entry.getKey();
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break;
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}
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}
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assert nextNode != null;
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final String edgeKey = currentNode.id + " -> " + nextNode.id;
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final int edgeTimes = usedEdges.getOrDefault(edgeKey, 0) + 1;
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usedEdges.put(edgeKey, edgeTimes);
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path.add(nextNode.id);
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currentNode = nextNode;
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if (edgeTimes >= 2) {
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break;
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}
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}
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return path;
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}
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public String toDOT(final Function<EdgeRecord, String> callback) {
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final var sb = new StringBuilder();
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sb.append("digraph G {\n");
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for (final Node node : nodes.values()) {
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for (final String edge : node.getDOTEdges(callback)) {
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sb.append(" ").append(edge);
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}
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}
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sb.append("}");
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return sb.toString();
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}
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public String toDOT() {
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final var sb = new StringBuilder();
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sb.append("digraph G {\n");
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for (final Node node : nodes.values()) {
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for (final String edge : node.getDOTEdges()) {
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sb.append(" ").append(edge).append("\n");
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}
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}
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sb.append("}");
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return sb.toString();
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}
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private void parse(final String input) {
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final String[] tokens = input.toLowerCase(Locale.ENGLISH).split("[ \n\r]+");
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final var words = new ArrayList<String>();
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for (final var token : tokens) {
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final String word = token.replaceAll("[^a-zA-Z]", "");
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if (!word.isEmpty()) {
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words.add(word);
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}
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}
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for (int i = 0; i < words.size() - 1; i++) {
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final String currentWord = words.get(i);
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final String nextWord = words.get(i + 1);
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final Node currentNode = getOrCreateNode(currentWord);
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final Node nextNode = getOrCreateNode(nextWord);
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currentNode.addEdge(nextNode);
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}
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}
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private Node getOrCreateNode(final String word) {
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return nodes.computeIfAbsent(word, Node::new);
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}
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private void initRageRanks(final double d) {
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final int totalNodes = nodes.size();
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if (totalNodes == 0) {
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pageRanks = new HashMap<>();
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return;
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}
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var myPageRanks = new HashMap<Node, Double>();
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final double initRank = 1.0 / totalNodes;
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for (final var n : nodes.values()) {
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myPageRanks.put(n, initRank);
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}
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final int iterations = 100;
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for (int i = 0; i < iterations; i++) {
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final var newPageRanks = new HashMap<Node, Double>();
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nodes.values().forEach(n -> newPageRanks.put(n, 0.0));
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for (final var curr : nodes.values()) {
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final int totalEdges = curr.edges.size();
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for (final var entry : curr.edges.entrySet()) {
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final Node neighbor = entry.getKey();
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final double contribution = myPageRanks.get(curr) / totalEdges;
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newPageRanks.put(neighbor, newPageRanks.get(neighbor) + contribution);
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}
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}
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final double damplingTerm = (1.0 - d) / totalNodes;
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nodes.values().forEach(n -> newPageRanks.put(n, damplingTerm + d * newPageRanks.get(n)));
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myPageRanks = newPageRanks;
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}
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pageRanks = myPageRanks;
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for (final var node : nodes.values()) {
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if (node.edges.isEmpty()) {
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nodes.values().stream().filter(n -> !n.equals(node))
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.forEach(n -> pageRanks.put(n, pageRanks.get(n) + pageRanks.get(node) / (totalNodes - 1)));
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pageRanks.put(node, 0.0);
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}
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}
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}
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}
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0
app/src/test/java/fun/youthlic/GraphTest.java
Normal file
0
app/src/test/java/fun/youthlic/GraphTest.java
Normal file
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