Graph.java

package Graph;

import java.util.ArrayList;
import java.util.HashMap;

public class Graph {

    private HashMap<String, ArrayList<String>> adjList = new HashMap<>();

    public boolean addVertex(String vertex){
        if (adjList.get(vertex)==null){
            adjList.put(vertex, new ArrayList<String>());
            return true;
        }
        return false;
    }

    public boolean addEdge(String vertex1, String vertex2){
        if (adjList.get(vertex1) !=null && adjList.get(vertex2) != null){
            adjList.get(vertex1).add(vertex2);
            adjList.get(vertex2).add(vertex1);
            return true;
        }
        return false;
    }

    public boolean removeEdge(String vertex1, String vertex2){
        if (adjList.get(vertex1) !=null && adjList.get(vertex2) != null){
            adjList.get(vertex1).remove(vertex2);
            adjList.get(vertex2).remove(vertex1);
            return true;
        }
        return false;
    }

    public boolean removeVertex(String vertex){
        if (adjList.get(vertex) == null) return false;
        for (String otherVertex:adjList.get(vertex)) {
            adjList.get(otherVertex).remove(vertex);
        }
        adjList.remove(vertex);
        return true;
    }

    public void printGraph(){
        System.out.println(adjList);
    }
}