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src/main/java/com/packt/datastructuresandalg/lesson6/dijkstra/Dijkstra.java
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package com.packt.datastructuresandalg.lesson6.dijkstra; | ||
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import java.lang.reflect.Array; | ||
import java.util.ArrayList; | ||
import java.util.HashSet; | ||
import java.util.List; | ||
import java.util.Set; | ||
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public class Dijkstra { | ||
private class Edge { | ||
int v; | ||
int weight; | ||
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Edge(int v, int weight) { | ||
this.v = v; | ||
this.weight = weight; | ||
} | ||
} | ||
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private class Vertex { | ||
int u; | ||
int distance; | ||
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Vertex(int u, int distance) { | ||
this.distance = distance; | ||
this.u = u; | ||
} | ||
} | ||
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public class Path { | ||
int from; | ||
int to; | ||
int distance; | ||
List<Integer> path; | ||
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Path(int from, int to, int distance, List<Integer> path) { | ||
this.from = from; | ||
this.to = to; | ||
this.distance = distance; | ||
this.path = path; | ||
} | ||
} | ||
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List<Edge> adj[]; | ||
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public Dijkstra(int nodes) { | ||
this.adj = new ArrayList[nodes]; | ||
for (int i = 0; i < nodes; i++) | ||
this.adj[i] = new ArrayList<>(); | ||
} | ||
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public void addEdge(int u, int v, int weight) { | ||
adj[u].add(new Edge(v, weight)); | ||
} | ||
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private Vertex getBestEstimate(Set<Vertex> vertices) { | ||
Vertex best = null; | ||
for (Vertex v : vertices) { | ||
if (best == null || v.distance < best.distance) | ||
best = v; | ||
} | ||
return best; | ||
} | ||
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public Path[] dijkstra(int source) { | ||
Set<Vertex> notVisited = new HashSet<>(); | ||
Set<Vertex> visited = new HashSet<>(); | ||
Vertex vertices[] = new Vertex[adj.length]; | ||
int parent[] = new int[adj.length]; | ||
for (int i = 0; i < adj.length; i++) { | ||
Vertex v = new Vertex(i, Integer.MAX_VALUE); | ||
vertices[i] = v; | ||
parent[i] = -1; | ||
notVisited.add(v); | ||
} | ||
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vertices[source].distance = 0; | ||
while (!notVisited.isEmpty()) { | ||
Vertex v = getBestEstimate(notVisited); | ||
notVisited.remove(v); | ||
visited.add(v); | ||
for (Edge e : adj[v.u]) { | ||
if (!visited.contains(e.v)) { | ||
Vertex next = vertices[e.v]; | ||
if (v.distance + e.weight < next.distance) { | ||
next.distance = v.distance + e.weight; | ||
parent[next.u] = v.u; | ||
} | ||
} | ||
} | ||
} | ||
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Path[] paths = new Path[adj.length]; | ||
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for (int i = 0; i < adj.length; i++) { | ||
List<Integer> path = new ArrayList<>(); | ||
Path p = new Path(source, i, vertices[i].distance, path); | ||
int j = i; | ||
while (parent[j] != -1) { | ||
path.add(0, j); | ||
j = parent[j]; | ||
} | ||
paths[i] = p; | ||
} | ||
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return paths; | ||
} | ||
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public static void main(String [] args) { | ||
Dijkstra d = new Dijkstra(5); | ||
d.addEdge(0, 1, 10); | ||
d.addEdge(0, 3, 5); | ||
d.addEdge(1, 3, 2); | ||
d.addEdge(1, 2, 1); | ||
d.addEdge(2, 4, 4); | ||
d.addEdge(3, 1, 3); | ||
d.addEdge(3, 2, 9); | ||
d.addEdge(3, 4, 2); | ||
d.addEdge(4, 2, 6); | ||
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Path[] paths = d.dijkstra(0); | ||
for (int i = 0; i < paths.length; i++) { | ||
Path p = paths[i]; | ||
System.out.print("Path from " + p.from + " to " + p.to + " (" + p.distance + ")"); | ||
for (int j = 0; j < p.path.size(); j++) { | ||
System.out.print(" " + p.path.get(j)); | ||
} | ||
System.out.println(); | ||
} | ||
} | ||
} |