Implement the RandomizedSet class:
RandomizedSet() Initializes the RandomizedSet object.
bool insert(int val)Inserts an item val into the set if not present. Returnstrueif the item was not present, false otherwise.bool remove(int val)Removes an item val from the set if present. Returnstrueif the item was present, false otherwise.int getRandom()Returns a random element from the current set of elements (it’s guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned.
You must implement the functions of the class such that each function works in average O(1) time complexity.
Test Cases
Example 1:
Input
["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"]
[[], [1], [2], [2], [], [1], [2], []]
Output
[null, true, false, true, 2, true, false, 2]
Explanation
RandomizedSet randomizedSet = new RandomizedSet();
randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomizedSet.remove(2); // Returns false as 2 does not exist in the set.
randomizedSet.insert(2); // Inserts 2 to the set, returns true. Set now contains [1,2].
randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly.
randomizedSet.remove(1); // Removes 1 from the set, returns true. Set now contains [2].
randomizedSet.insert(2); // 2 was already in the set, so return false.
randomizedSet.getRandom(); // Since 2 is the only number in the set, getRandom() will always return 2.
Solution
class RandomizedSet {
private Random random;
private Map<Integer, Integer> map;
private List<Integer> arr;
public RandomizedSet() {
random = new Random();
map = new HashMap<>();
arr = new ArrayList<>();
}
public boolean insert(int val) {
if (map.containsKey(val)) return false;
map.put(val, arr.size());
arr.add(val);
return true;
}
public boolean remove(int val) {
if (!map.containsKey(val)) return false;
int pos = map.get(val);
if (pos < arr.size() - 1) {
int lastElement = arr.get(arr.size() - 1);
map.put(lastElement, pos);
arr.set(pos, lastElement);
}
map.remove(val);
arr.remove(arr.size() - 1);
return true;
}
public int getRandom() {
return arr.get(random.nextInt(arr.size()));
}
}
/**
* Your RandomizedSet object will be instantiated and called as such:
* RandomizedSet obj = new RandomizedSet();
* boolean param_1 = obj.insert(val);
* boolean param_2 = obj.remove(val);
* int param_3 = obj.getRandom();
*/