11.20

import java.util.*;

// 1. 边类：存储目标顶点和权重
class Edge {
int targetVertex; // 目标顶点的索引
int weight; // 边的权重（无权图可设为1）

public Edge(int targetVertex, int weight) {
    this.targetVertex = targetVertex;
    this.weight = weight;
}

}

// 2. 图类（邻接表实现）
class Graph {
private List vertices; // 存储顶点数据（如 "A", "B"）
private List<List> adjacencyList; // 邻接表：index=顶点索引，value=该顶点的所有边

// 初始化空图
public Graph() {
    vertices = new ArrayList<>();
    adjacencyList = new ArrayList<>();
}