leetcode/work/1/Medium/Array/380.insert-delete-getrandom-o1.py

"""
380. Insert Delete GetRandom O(1)
Difficulty: Medium
https://leetcode.com/problems/insert-delete-getrandom-o1/

──────────────────────────────────────────────────

Implement the RandomizedSet class:

        • RandomizedSet() Initializes the RandomizedSet object.

• bool insert(int val) Inserts an item val into the set if not
present. Returns true if the item was not present, false otherwise.

• bool remove(int val) Removes an item val from the set if present.
Returns true if 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.



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.



Constraints:

        • -2^31 <= val <= 2^31 - 1

• At most 2 * 10^5 calls will be made to insert, remove, and
getRandom.

• There will be at least one element in the data structure when
getRandom is called.
"""

from random import choice


class RandomizedSet:
    def __init__(self):
        self.list = []
        self.dict = {}

    def insert(self, val: int) -> bool:
        if val in self.dict:
            return False
        self.dict[val] = len(self.list)
        self.list.append(val)
        return True

    def remove(self, val: int) -> bool:
        if val in self.dict:
            last, idx = self.list[-1], self.dict[val]
            self.list[idx], self.dict[last] = last, idx
            self.list.pop()
            del self.dict[val]
            return True
        return False

    def getRandom(self) -> int:
        return choice(self.list)


# 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()