Collectables_ipynb_2_

import java.util.*;

class Queueing {
    public static void main(String[] args) {
        ArrayDeque<Integer> deque = new ArrayDeque<>();

        for(int i=0; i<20; i++){
            if(i%2 == 0){
                deque.addFirst(i);
            }else{
                deque.addLast(i);
            }
        }
        System.out.println(deque.toString());

        for(int i=0; i<20; i++){
            if(i%2 == 0){
                deque.removeFirst();
            }else{
                deque.removeLast();
            }
        }

        System.out.println(deque.size());
    }
}

Queueing.main(null);

import java.util.*;

class Hashing {
    static String getKeyFromValue(HashMap<String,String> map, String value){
        String result = "";
        Iterator<String> mapKeys = map.keySet().iterator();
        while(mapKeys.hasNext()){
            String key = mapKeys.next();

            if(map.get(key).equals(value)){
                return key;
            }

        }
        return null;
    }

    public static void main(String[] args){
        HashMap<String,String> map = new HashMap<>();

        map.put("Person 1","123456789");
        map.put("Person 2","192837465");
        map.put("Person 3","987654321");
        map.put("Person 4","123465789");
        map.put("Person 5","543216789");


        System.out.println(Hashing.getKeyFromValue(map, "543216789"));
    }
}

Hashing.main(null);