package ru.kpfu.dfs.graph.impl;

import ru.kpfu.dfs.graph.Graph;

import java.util.LinkedList;
import java.util.List;

/**
 * @author Alexeev Vladimir  27.04.2015
 */
public class ListGraph implements Graph{

    private List<Integer>[] list;
    private List<Integer> blankList;

    private ListGraph() {}

    public ListGraph(int count) {
        list = new List[count];
    }

    @Override
    public void joinVertices(int from, int to) {
        if(from >= list.length || to >= list.length) return;
        if(list[from] == null) list[from] = new LinkedList<>();
        list[from].add(to);
        if(list[to] == null) list[to] = new LinkedList<>();
        list[to].add(from);
    }

    @Override
    public List<Integer> adjacentVertices(int vertex) {
        if(list[vertex] == null) {
            if(blankList == null) blankList = new LinkedList<>();
            return blankList;
        }
        return list[vertex];
    }

    @Override
    public int size() {
        return list.length;
    }
}