B2.java

importjava.util.*;

publicclassB2 {
publicstaticclassRandomHashMap<K, V> {
privateMap<K, V> hm;
privateList<K> keys;
privateRandomgenerator;

publicRandomHashMap() {
hm = newHashMap<K, V>();
keys = newArrayList<K>();
generator = newRandom();
 }

publicVget(Kkey) {
returnhm.get(key);
 }

publicvoidput(Kkey, Vvalue) {
if (hm.get(key) == null) {
keys.add(key);
 }

hm.put(key, value);
 }

publicbooleanremove(Kkey) {
if (hm.get(key) == null) {
returnfalse;
 }

for (inti = 0; i < keys.size(); i++) {
if (keys.get(i).equals(key)) {
keys.remove(i);
 }
 }

hm.remove(key);
returntrue;
 }

publicKgetRandomKey() {
if (hm.size() == 0) {
returnnull;
 }

intidx = generator.nextInt(hm.size());
returnkeys.get(idx);
 }
 }

publicstaticvoidmain(String[] args) {
RandomHashMap<String, Integer> hm = newRandomHashMap<>();

System.out.println(hm.getRandomKey());

hm.put("A", 1);
hm.put("B", 2);
hm.put("C", 3);
hm.put("D", 4);

for (inti = 0; i < 5; i++) {
System.out.println(hm.getRandomKey());
 }

System.out.println(hm.get("C"));
System.out.println(hm.get("A"));

System.out.println(hm.remove("A"));
System.out.println(hm.remove("Null"));

return;
 }
}