programming-examples/java/Graph_Problems_Algorithms/Java Program to Implement Uniform-Cost Search.java

/*This Java program,Implements Uniform Cost Search.In computer science, uniform-cost search (UCS) is a tree search algorithm used for traversing or searching a weighted tree, tree structure, or graph. The search begins at the root node. The search continues by visiting the next node which has the least total cost from the root. Nodes are visited in this manner until a goal state is reached.*/

import java.util.Comparator;
import java.util.HashSet;
import java.util.InputMismatchException;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Scanner;
import java.util.Set;

public class UniformCostSearch
{
    private PriorityQueue<Node> priorityQueue;
    private Set<Integer> settled;
    private int distances[];
    private int numberOfNodes;
    private int adjacencyMatrix[][];
    private LinkedList<Integer> path;
    private int[] parent;
    private int source, destination;
    public static final int MAX_VALUE = 999;

    public UniformCostSearch(int numberOfNodes)
    {
        this.numberOfNodes = numberOfNodes;
        this.settled = new HashSet<Integer>();
        this.priorityQueue = new PriorityQueue<>(numberOfNodes, new Node());
        this.distances = new int[numberOfNodes + 1];
        this.path = new LinkedList<Integer>();
        this.adjacencyMatrix = new int[numberOfNodes + 1][numberOfNodes + 1];
        this.parent = new int[numberOfNodes + 1];
    }

    public int uniformCostSearch(int adjacencyMatrix[][], int source, int destination)
    {
        int evaluationNode;
        this.source = source;
        this.destination = destination;
        for (int i = 1; i <= numberOfNodes; i++)
            {
                distances[i] = MAX_VALUE;
            }
        for (int sourcevertex = 1; sourcevertex <= numberOfNodes; sourcevertex++)
            {
                for (int destinationvertex = 1; destinationvertex <= numberOfNodes; destinationvertex++)
                    {
                        this.adjacencyMatrix[sourcevertex][destinationvertex] =
                            adjacencyMatrix[sourcevertex[destinationvertex];
                    }
            }
        priorityQueue.add(new Node(source, 0));
        distances[source] = 0;
        while (!priorityQueue.isEmpty())
            {
                evaluationNode = getNodeWithMinDistanceFromPriorityQueue();
                System.out.println("The eval Node is " + evaluationNode);
                if (evaluationNode == destination)
                    {
                        return distances[destination];
                    }
                settled.add(evaluationNode);
                addFrontiersToQueue(evaluationNode);
            }
        return distances[destination];
    }

    private void addFrontiersToQueue(int evaluationNode)
    {
        for (int destination = 1; destination <= numberOfNodes; destination++)
            {
                if (!settled.contains(destination))
                    {
                        if (adjacencyMatrix[evaluationNode][destination] != MAX_VALUE)
                            {
                                if (distances[destination] > adjacencyMatrix[evaluationNode][destination]
                                        + distances[evaluationNode])
                                    {
                                        distances[destination] = adjacencyMatrix[evaluationNode][destination]
                                                                 + distances[evaluationNode];
                                        parent[destination] = evaluationNode;
                                    }
                                Node node = new Node(destination, distances[destination]);
                                if (priorityQueue.contains(node))
                                    {
                                        priorityQueue.remove(node);
                                    }
                                priorityQueue.add(node);
                            }
                    }
            }
    }

    private int getNodeWithMinDistanceFromPriorityQueue()
    {
        Node node = priorityQueue.remove();
        return node.node;
    }

    public void printPath()
    {
        path.add(destination);
        boolean found = false;
        int vertex = destination;
        while (!found)
            {
                if (vertex == source)
                    {
                        found = true;
                        continue;
                    }
                path.add(parent[vertex]);
                vertex = parent[vertex];
            }
        System.out.println("The Path between " + source + " and " + destination+ " is ");
        Iterator<Integer> iterator = path.descendingIterator();
        while (iterator.hasNext())
            {
                System.out.print(iterator.next() + "\t");
            }
    }

    public static void main(String... arg)
    {
        int adjacency_matrix[][];
        int number_of_vertices;
        int source = 0;
        int destination = 0;
        int distance;
        Scanner scan = new Scanner(System.in);
        try
            {
                System.out.println("Enter the number of vertices");
                number_of_vertices = scan.nextInt();
                adjacency_matrix = new int[number_of_vertices + 1][number_of_vertices + 1];
                System.out.println("Enter the Weighted Matrix for the graph");
                for (int i = 1; i <= number_of_vertices; i++)
                    {
                        for (int j = 1; j <= number_of_vertices; j++)
                            {
                                adjacency_matrix[i][j] = scan.nextInt();
                                if (i == j)
                                    {
                                        adjacency_matrix[i][j] = 0;
                                        continue;
                                    }
                                if (adjacency_matrix[i][j] == 0)
                                    {
                                        adjacency_matrix[i][j] = MAX_VALUE;
                                    }
                            }
                    }
                System.out.println("Enter the source ");
                source = scan.nextInt();
                System.out.println("Enter the destination");
                destination = scan.nextInt();
                UniformCostSearch uniformCostSearch = new UniformCostSearch(number_of_vertices);
                distance = uniformCostSearch.uniformCostSearch(adjacency_matrix,source, destination);
                uniformCostSearch.printPath();
                System.out.println("\nThe Distance between source " + source +
                                   " and destination " + destination + " is " + distance);
            }
        catch (InputMismatchException inputMismatch)
            {
                System.out.println("Wrong Input Format");
            }
        scan.close();
    }
}

class Node implements Comparator<Node>
{
    public int node;
    public int cost;

    public Node()
    {
    }

    public Node(int node, int cost)
    {
        this.node = node;
        this.cost = cost;
    }

    @Override
    public int compare(Node node1, Node node2)
    {
        if (node1.cost < node2.cost)
            return -1;
        if (node1.cost > node2.cost)
            return 1;
        if (node1.node < node2.node)
            return -1;
        return 0;
    }

    @Override
    public boolean equals(Object obj)
    {
        if (obj instanceof Node)
            {
                Node node = (Node) obj;
                if (this.node == node.node)
                    {
                        return true;
                    }
            }
        return false;
    }
}

/*
Enter the number of vertices
7
Enter the Weighted Matrix for the graph
0 5 0 3 0 0 0
0 0 1 0 0 0 0
0 0 0 0 6 0 8
0 0 0 0 2 2 0
0 4 0 0 0 0 0
0 0 0 0 0 0 3
0 0 0 0 4 0 0
Enter the source
1
Enter the destination
7
The Path between 1 and 7 is
1	4	6	7
The Distance between source 1 and destination 7 is 8