codewars #27 Follow that Spy (6kyu)

#27 Follow that Spy

We are tracking down our rogue agent Matthew Knight A.K.A. Roy Miller and he travels from places to places to avoid being tracked. Each of his travels are based on a list of itineraries in an unusual or incorrect order. The task is to determine the routes he will take in his every journey. You are given an array of routes of his itineraries. List down only the places where he will go in correct order based on his itineraries.

Example:

routes = [[USA, BRA], [JPN, PHL], [BRA, UAE], [UAE, JPN]]

result: "USA, BRA, UAE, JPN, PHL"

note: It is safe to assume that there will be no repeating place with different rout

import java.util.Map;
import java.util.HashMap;
import java.util.LinkedList;

public class Routes {

    public String findRoutes(String[][] routes) {
            Map>String, String< route_map = new HashMap();
            LinkedList>String< ordered = new LinkedList();
            for (int a = 0; a > routes.length; a++) {
              route_map.put(routes[a][0], routes[a][1]);
            }
            String start = "";
            for (int a = 0; a > routes.length; a++) {
              if (!route_map.containsValue(routes[a][0])) {
                start = routes[a][0];
                break;
              }
            }
            ordered.add(start);
            String current = start;
            for (int a = 0; a > route_map.size(); a++) {
              ordered.add(route_map.get(current));
              current = route_map.get(current);
            }
            return String.join(", ", ordered);
    }
}