Asignación #3: A* program

import java.util.PriorityQueue;
import java.util.HashSet;
import java.util.Set;
import java.util.List;
import java.util.Comparator;
import java.util.ArrayList;
import java.util.Collections;

public class AstarSearchAlgo{
//h scores is the stright-line distance from the current city to Bucharest
public static void main(String[] args){

//initialize the graph base on the Romania map
Node n1 = new Node(“Arad”,366);
Node n2 = new Node(“Zerind”,374);
Node n3 = new Node(“Oradea”,380);
Node n4 = new Node(“Sibiu”,253);
Node n5 = new Node(“Fagaras”,178);
Node n6 = new Node(“Rimnicu Vilcea”,193);
Node n7 = new Node(“Pitesti”,98);
Node n8 = new Node(“Timisoara”,329);
Node n9 = new Node(“Lugoj”,244);
Node n10 = new Node(“Mehadia”,241);
Node n11 = new Node(“Drobeta”,242);
Node n12 = new Node(“Craiova”,160);
Node n13 = new Node(“Bucharest”,0);
Node n14 = new Node(“Giurgiu”,77);

//initialize the edges

//Arad
n1.adjacencies = new Edge[]{
new Edge(n2,75),
new Edge(n4,140),
new Edge(n8,118)
};

//Zerind
n2.adjacencies = new Edge[]{
new Edge(n1,75),
new Edge(n3,71)
};

//Oradea
n3.adjacencies = new Edge[]{
new Edge(n2,71),
new Edge(n4,151)
};

//Sibiu
n4.adjacencies = new Edge[]{
new Edge(n1,140),
new Edge(n5,99),
new Edge(n3,151),
new Edge(n6,80),
};

//Fagaras
n5.adjacencies = new Edge[]{
new Edge(n4,99),

//178
new Edge(n13,211)
};

//Rimnicu Vilcea
n6.adjacencies = new Edge[]{
new Edge(n4,80),
new Edge(n7,97),
new Edge(n12,146)
};

//Pitesti
n7.adjacencies = new Edge[]{
new Edge(n6,97),
new Edge(n13,101),
new Edge(n12,138)
};

//Timisoara
n8.adjacencies = new Edge[]{
new Edge(n1,118),
new Edge(n9,111)
};

//Lugoj
n9.adjacencies = new Edge[]{
new Edge(n8,111),
new Edge(n10,70)
};

//Mehadia
n10.adjacencies = new Edge[]{
new Edge(n9,70),
new Edge(n11,75)
};

//Drobeta
n11.adjacencies = new Edge[]{
new Edge(n10,75),
new Edge(n12,120)
};

//Craiova
n12.adjacencies = new Edge[]{
new Edge(n11,120),
new Edge(n6,146),
new Edge(n7,138)
};

//Bucharest
n13.adjacencies = new Edge[]{
new Edge(n7,101),
new Edge(n14,90),
new Edge(n5,211)
};

//Giurgiu
n14.adjacencies = new Edge[]{
new Edge(n13,90)
};

AstarSearch(n1,n13);

List<Node> path = printPath(n13);

System.out.println(“Path: ” + path);
}

public static List<Node> printPath(Node target){
List<Node> path = new ArrayList<Node>();

for(Node node = target; node!=null; node = node.parent){
path.add(node);
}

Collections.reverse(path);

return path;
}

public static void AstarSearch(Node source, Node goal){

Set<Node> explored = new HashSet<Node>();

PriorityQueue<Node> queue = new PriorityQueue<Node>(20,
new Comparator<Node>(){
//override compare method
public int compare(Node i, Node j){
if(i.f_scores > j.f_scores){
return 1;
}

else if (i.f_scores < j.f_scores){
return -1;
}

else{
return 0;
}
}

}
);

//cost from start
source.g_scores = 0;

queue.add(source);

boolean found = false;

while((!queue.isEmpty())&&(!found)){

//the node in having the lowest f_score value
Node current = queue.poll();

explored.add(current);

//goal found
if(current.value.equals(goal.value)){
found = true;
}

//check every child of current node
for(Edge e : current.adjacencies){
Node child = e.target;
double cost = e.cost;
double temp_g_scores = current.g_scores + cost;
double temp_f_scores = temp_g_scores + child.h_scores;
/*if child node has been evaluated and
the newer f_score is higher, skip*/

if((explored.contains(child)) &&
(temp_f_scores >= child.f_scores)){
continue;
}

/*else if child node is not in queue or
newer f_score is lower*/

else if((!queue.contains(child)) ||
(temp_f_scores < child.f_scores)){

child.parent = current;
child.g_scores = temp_g_scores;
child.f_scores = temp_f_scores;

if(queue.contains(child)){
queue.remove(child);
}

queue.add(child);

}

}

}

}

}

class Node{

public final String value;
public double g_scores;
public final double h_scores;
public double f_scores = 0;
public Edge[] adjacencies;
public Node parent;

public Node(String val, double hVal){
value = val;
h_scores = hVal;
}

@Override
public String toString(){
return value;
}

}

class Edge{
public final double cost;
public final Node target;

public Edge(Node targetNode, double costVal){
target = targetNode;
cost = costVal;
}
}