public class GraphAdjacentList {

    private Node listMatrix[];
    private int numVertices;

    class Node {
        public Node next;
        public int vertice;
        public Node(int v){
            this.vertice = v;
        }
    }

    public GraphAdjacentList(int numVertices) {
        this.numVertices = numVertices;
        listMatrix = new Node[numVertices];
        for (int i = 0 ; i < numVertices; i++) {
            this.listMatrix[i] = new Node(i);
        }
    }

    public void setEdge(int i, int j) {
        Node lastNode = null;
        lastNode = listMatrix[i];
        while (lastNode.next != null) {
            lastNode = lastNode.next;
        }
        lastNode.next = new Node(j);

        lastNode = listMatrix[j];
        while (lastNode.next != null) {
            lastNode = lastNode.next;
        }
        lastNode.next = new Node(i);
    }

    public void delEdge(int i, int j) {
        Node currNode = null;
        currNode = listMatrix[i];
        while (true) {
            if (currNode.next.vertice == j) break;
            if (currNode == null) break;
            currNode = currNode.next;
        }
        if (currNode != null) {
            currNode.next = currNode.next.next;
        }

        currNode = listMatrix[j];
        while (true) {
            if (currNode.next.vertice == i) break;
            if (currNode == null) break;
            currNode = currNode.next;
        }
        if (currNode != null) {
            currNode.next = currNode.next.next;
        }
    }

    public boolean isEdge(int i, int j) {
        Node currNode = null;
        currNode = listMatrix[i];
        while (true) {
            if (currNode == null) break;
            if (currNode.vertice == j) return true;
            currNode = currNode.next;
        }
        return false;
    }

    public int first(int v1){
        Node currNode = listMatrix[v1];
        int firstNeighborIndex = this.numVertices; // return n if none
        if (currNode.next != null){
            return currNode.next.vertice;
        }
        return firstNeighborIndex;
    }

    public int next(int v1, int v2){
        int firstNeighborIndex = this.numVertices; // return n if none
        Node currNode = listMatrix[v1];
        while (true) {
            if (currNode == null) break;
            if (currNode.vertice == v2 && currNode.next != null) return currNode.next.vertice;
            currNode = currNode.next;
        }
        return firstNeighborIndex;
    }

    public static void main(String[] args) {
        GraphAdjacentList gam = new GraphAdjacentList(5);
        boolean isEdge;
        gam.setEdge(0, 1);
        isEdge = gam.isEdge(0, 1);
        gam.delEdge(0, 1);
        isEdge = gam.isEdge(0, 1);

        gam.setEdge(0, 1);
        gam.setEdge(0, 2);
        gam.setEdge(0, 4);

        int nextNeighbor;
        nextNeighbor = gam.first(0);
        nextNeighbor = gam.next(0, nextNeighbor);
        nextNeighbor = gam.next(0, nextNeighbor);
        nextNeighbor = gam.next(0, nextNeighbor);

        System.out.print(gam.toString());
        System.out.println();
    }

}