a_184_Ticket.java

import java.util.* ;

public class a_184_Ticket {

    public static String getStart(HashMap<String,String> tickets){
        HashMap<String,String> revMap = new HashMap<>() ;

        for(String key : tickets.keySet()){
            revMap.put(tickets.get(key), key ) ;
        }

        for(String key : tickets.keySet()) {
            if(!revMap.containsKey(key)){
                return key ;    // Starting point 
            }
        }

        return null ;
    }

    public static void main(String[] args) {

        HashMap<String ,String> tickets = new HashMap<>() ;
        tickets.put("Chennai", "Bangalure") ;
        tickets.put("Mumabi", "Delhi") ;
        tickets.put("Goa", "chennai") ;
        tickets.put("Delhi", "Goa") ;

        String start = getStart(tickets) ;
        System.out.print(start);

        // for(String key : tickets.keySet()) {
        //     System.out.print(" -> " + tickets.get(start));
        //     start = tickets.get(start) ;
        // }

        // System.out.println();

        
        
    }
}