LeetCode 380---Insert Delete GetRandom O(1)

package com.leetcode.arrays;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Random;

public class Problem380 {

HashMap<Integer,Integer> map = new HashMap<>();
ArrayList<Integer> arr = new ArrayList<>();
/** Initialize your data structure here. */
public Problem380() {
}

/** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
public boolean insert(int val) {
if(!map.containsKey(val)){
map.put(val,1);
arr.add(val);
return true;
}
return false;
}

/** Removes a value from the set. Returns true if the set contained the specified element. */
public boolean remove(int val) {
if(map.containsKey(val)){
map.remove(val);
arr.remove(arr.indexOf(val));
return true;
}
return false;
}

/** Get a random element from the set. */
public int getRandom() {
if(arr.size() != 0){
Random rm=new Random();
int val = rm.nextInt(arr.size());
return arr.get(val);
}
return 0;
}
}