// IncidenceList.java

import java.util.LinkedList;

class Graph {
    // a class for storing an edge of the graph
    private class Edge {
        public int to;
        public int cost;

        public Edge(int to, int cost) {
            this.to = to;
            this.cost = cost;
        }

        // this is so we can search for edges by destination
        public boolean equals(Object other) {
            Edge otherEdge = (Edge) other;
            return to == otherEdge.to;
        }
    }

    // an array of linked lists, each list holds the edges out of that node
    private LinkedList<Edge>[] nodes;

    // construct an empty graph of a given size
    public Graph(int size) {
        // becasue this is a generic array, we need to cast
        nodes = (LinkedList<Edge>[]) new LinkedList[size];
        
        for (int i = 0; i < size; i++) {
            nodes[i] = new LinkedList<Edge>();
        }
    }

    // insert an edge
    public void insert(int from, int to, int cost) {
        nodes[from].add(new Edge(to, cost));
    }

    // remove an edge
    public void remove(int from, int to) {
        nodes[from].remove(new Edge(to, -1));
    }

    // return the cost of an edge or 0 for none
    public int getCost(int from, int to) {
        // search the linked list for this edge
        int index = nodes[from].indexOf(new Edge(to, -1));
        
        // if -1, return 0
        // else return the cost of that edge
        if (index == -1) {
            return 0;
        } else {
            return nodes[from].get(index).cost;
        }
    }
}

public class IncidenceList {
    public static void main(String args[]) {
        // create a graph with 6 nodes
        Graph graph = new Graph(6);

        // add the edges
        graph.insert(0, 3, 15);
        graph.insert(0, 4, 20);

        graph.insert(1, 5, 25);

        graph.insert(3, 0, 15);
        graph.insert(3, 1, 25);

        graph.insert(4, 2, 30);
        graph.insert(4, 5, 10);

        graph.insert(5, 1, 25);
    }
}