带有字符串输入的顺序依赖（拓扑排序）

Question

https://leetcode.com/problems/course-schedule-ii/ 问题类似于这个问题，但它输入的是字符串而不是数字。以下是类和示例测试用例和签名。我只是想知道如何处理字符串

的输入

import java.util.*;
class Order{
    String order = "";
    public Order(String string){
        this.order = string;
    }
}
class OrderDependency{
    Order cur;
    Order pre;
    public OrderDependency(Order o1, Order o2){
        cur = o1;
        pre = o2;
    }
}
public class Order_Dependency {
    public static List<Order> getOrderList(List<OrderDependency> orderDependencies){

    ***Code Starts Here***

    }
    public static void main(String[] args) {
        Order o1 = new Order("A");
        Order o2 = new Order("B");
        Order o3 = new Order("C");
        Order o4 = new Order("D");
        OrderDependency od1 = new OrderDependency(o1, o2);
        OrderDependency od2 = new OrderDependency(o2, o3);
        OrderDependency od3 = new OrderDependency(o3, o4);
        List<OrderDependency> list = new ArrayList<>();
        list.add(od1);
        list.add(od2);
        list.add(od3);

        for (Order o : getOrderList(list)){
            System.out.println(o.order);
        }
    }
}