Insert Delete GetRandom O(1) LeetCode solution in Java

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class RandomizedSet {
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  HashMap<Integer, Integer> map;
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  ArrayList<Integer> list;
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  Random rand;
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  public RandomizedSet() {
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    map = new HashMap<>();
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    list = new ArrayList<>();
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    rand = new Random();
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  }
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  public boolean insert(int val) {
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    if (!map.containsKey(val)) {
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      map.put(val, list.size());
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      list.add(val);
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      return true;
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    }
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    return false;
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  }
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  public boolean remove(int val) {
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    if (map.containsKey(val)) {
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      int index = map.get(val);
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      int last = list.get(list.size() - 1);
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      if (index != list.size() - 1) {
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        list.set(index, last);
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        map.put(last, index);
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      }
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      list.remove(list.size() - 1);
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      map.remove(val);
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      return true;
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    }
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    return false;
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  }
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  public int getRandom() {
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    int r = rand.nextInt(list.size());
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    return list.get(r);
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  }
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}