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Java's implementation of Dijkstra's Algorithm
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import java.util.PriorityQueue; | |
import java.util.List; | |
import java.util.ArrayList; | |
import java.util.Collections; | |
public class DijkstraAlgo{ | |
/* Dijkstra Algorithm | |
* | |
* | |
*/ | |
public static void computePaths(Node source){ | |
source.shortestDistance=0; | |
//implement a priority queue | |
PriorityQueue<Node> queue = new PriorityQueue<Node>(); | |
queue.add(source); | |
while(!queue.isEmpty()){ | |
Node u = queue.poll(); | |
/*visit the adjacencies, starting from | |
the nearest node(smallest shortestDistance)*/ | |
for(Edge e: u.adjacencies){ | |
Node v = e.target; | |
double weight = e.weight; | |
//relax(u,v,weight) | |
double distanceFromU = u.shortestDistance+weight; | |
if(distanceFromU<v.shortestDistance){ | |
/*remove v from queue for updating | |
the shortestDistance value*/ | |
queue.remove(v); | |
v.shortestDistance = distanceFromU; | |
v.parent = u; | |
queue.add(v); | |
} | |
} | |
} | |
} | |
public static List<Node> getShortestPathTo(Node target){ | |
//trace path from target to source | |
List<Node> path = new ArrayList<Node>(); | |
for(Node node = target; node!=null; node = node.parent){ | |
path.add(node); | |
} | |
//reverse the order such that it will be from source to target | |
Collections.reverse(path); | |
return path; | |
} | |
public static void main(String[] args){ | |
//initialize the graph base on the Romania map | |
Node n1 = new Node("Arad"); | |
Node n2 = new Node("Zerind"); | |
Node n3 = new Node("Oradea"); | |
Node n4 = new Node("Sibiu"); | |
Node n5 = new Node("Fagaras"); | |
Node n6 = new Node("Rimnicu Vilcea"); | |
Node n7 = new Node("Pitesti"); | |
Node n8 = new Node("Timisoara"); | |
Node n9 = new Node("Lugoj"); | |
Node n10 = new Node("Mehadia"); | |
Node n11 = new Node("Drobeta"); | |
Node n12 = new Node("Craiova"); | |
Node n13 = new Node("Bucharest"); | |
Node n14 = new Node("Giurgiu"); | |
//initialize the edges | |
n1.adjacencies = new Edge[]{ | |
new Edge(n2,75), | |
new Edge(n4,140), | |
new Edge(n8,118) | |
}; | |
n2.adjacencies = new Edge[]{ | |
new Edge(n1,75), | |
new Edge(n3,71) | |
}; | |
n3.adjacencies = new Edge[]{ | |
new Edge(n2,71), | |
new Edge(n4,151) | |
}; | |
n4.adjacencies = new Edge[]{ | |
new Edge(n1,140), | |
new Edge(n5,99), | |
new Edge(n3,151), | |
new Edge(n6,80), | |
}; | |
n5.adjacencies = new Edge[]{ | |
new Edge(n4,99), | |
new Edge(n13,211) | |
}; | |
n6.adjacencies = new Edge[]{ | |
new Edge(n4,80), | |
new Edge(n7,97), | |
new Edge(n12,146) | |
}; | |
n7.adjacencies = new Edge[]{ | |
new Edge(n6,97), | |
new Edge(n13,101), | |
new Edge(n12,138) | |
}; | |
n8.adjacencies = new Edge[]{ | |
new Edge(n1,118), | |
new Edge(n9,111) | |
}; | |
n9.adjacencies = new Edge[]{ | |
new Edge(n8,111), | |
new Edge(n10,70) | |
}; | |
n10.adjacencies = new Edge[]{ | |
new Edge(n9,70), | |
new Edge(n11,75) | |
}; | |
n11.adjacencies = new Edge[]{ | |
new Edge(n10,75), | |
new Edge(n12,120) | |
}; | |
n12.adjacencies = new Edge[]{ | |
new Edge(n11,120), | |
new Edge(n6,146), | |
new Edge(n7,138) | |
}; | |
n13.adjacencies = new Edge[]{ | |
new Edge(n7,101), | |
new Edge(n14,90), | |
new Edge(n5,211) | |
}; | |
n14.adjacencies = new Edge[]{ | |
new Edge(n13,90) | |
}; | |
Node[] nodes = {n1,n2,n3,n4,n5,n6,n7,n8,n9,n10,n11,n12,n13,n14}; | |
//compute paths | |
computePaths(n1); | |
//print shortest paths | |
/* | |
for(Node n: nodes){ | |
System.out.println("Distance to " + | |
n + ": " + n.shortestDistance); | |
List<Node> path = getShortestPathTo(n); | |
System.out.println("Path: " + path); | |
}*/ | |
List<Node> path = getShortestPathTo(n13); | |
System.out.println("Path: " + path); | |
} | |
} | |
//define Node | |
class Node implements Comparable<Node>{ | |
public final String value; | |
public Edge[] adjacencies; | |
public double shortestDistance = Double.POSITIVE_INFINITY; | |
public Node parent; | |
public Node(String val){ | |
value = val; | |
} | |
public String toString(){ | |
return value; | |
} | |
public int compareTo(Node other){ | |
return Double.compare(shortestDistance, other.shortestDistance); | |
} | |
} | |
//define Edge | |
class Edge{ | |
public final Node target; | |
public final double weight; | |
public Edge(Node targetNode, double weightVal){ | |
target = targetNode; | |
weight = weightVal; | |
} | |
} |
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Why do you make an array of nodes on line 159? This isn't called or used and serves no function