public class Graph<T> {

    // 연결리스트
    private Map<Vertex<T>, List<Vertex<T>>> adjVertices = new HashMap<>();

    void addVertex(T label){
        adjVertices.putIfAbsent(new Vertex(label),new ArrayList<>());
    }

    void removeVertex(T label){
        Vertex vertex = new Vertex(label);
        adjVertices.values().stream().forEach((e)->e.remove(vertex));
        adjVertices.remove(vertex);
    }

    void addEdge(T label1,T label2){
        Vertex<T> v1 = new Vertex(label1);
        Vertex<T> v2 = new Vertex(label2);
        adjVertices.get(v1).add(v2);
        adjVertices.get(v2).add(v1);
    }

    void removeEdge(T label1, T label2){
        Vertex v1 = new Vertex(label1);
        Vertex v2 = new Vertex(label2);
        List<Vertex<T>> vertices1 = adjVertices.get(v1);
        List<Vertex<T>> vertices2 = adjVertices.get(v2);
        if(vertices1 != null){
            vertices1.remove(v2);
        }
        if(vertices2 != null){
            vertices2.remove(v1);
        }
    }
    List<Vertex<T>> getAdjvertices(T label ){
         return adjVertices.get(new Vertex(label));
    }
    public class Vertex<T>{
        T label;
        Vertex(T label){
            this.label = label;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Vertex vertex = (Vertex) o;
            return Objects.equals(label, vertex.label);
        }

        @Override
        public int hashCode() {
            return Objects.hash(label);
        }
    }
}