380. Insert Delete GetRandom O\(1\)

380. Insert Delete GetRandom O(1)

class RandomizedSet:

    def __init__(self):
        Initialize your data structure here.
        self.table = {} # val to index
        self.arr = []

    def insert(self, val: int) -> bool:
        Inserts a value to the set. Returns true if the set did not already contain the specified element.
        if val in self.table:
            return False
        self.table[val] = len(self.arr)
        return True

    def remove(self, val: int) -> bool:
        Removes a value from the set. Returns true if the set contained the specified element.
        if val not in self.table:
            return False
        idx = self.table[val]
        self.table[self.arr[-1]] = idx
        self.arr[idx], self.arr[-1] = self.arr[-1], self.arr[idx]
        del self.table[val]
        return True

    def getRandom(self) -> int:
        Get a random element from the set.
        return self.arr[random.randint(0, len(self.arr)-1)]

# Your RandomizedSet object will be instantiated and called as such:
# obj = RandomizedSet()
# param_1 = obj.insert(val)
# param_2 = obj.remove(val)
# param_3 = obj.getRandom()