What is the time complexity of LeetCode 381. Insert Delete GetRandom O(1) - Duplicates allowed?

The Python solution on this page runs in O(n).

What is the space complexity of LeetCode 381. Insert Delete GetRandom O(1) - Duplicates allowed?

The Python solution on this page uses O(n) auxiliary space.

Insert Delete GetRandom O(1) - Duplicates allowed — LeetCode 381 Python Solution

HardDesignArrayHash TableMathRandomized

Problem: #381
Pattern: Math and Number Theory
Reading time: 9 min
Source: leetcode.com

The problem

RandomizedCollection is a data structure that contains a collection of numbers, possibly duplicates (i.e., a multiset). It should support inserting and removing specific elements and also reporting a random element.

Example

Input: ["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"]
Output: [null, true, false, true, 2, true, 1]
Explanation: RandomizedCollection randomizedCollection = new RandomizedCollection();

Python solution

Python

class RandomizedCollection:
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.m = {}
        self.l = []

    def insert(self, val: int) -> bool:
        """
        Inserts a value to the collection. Returns true if the collection did not already contain the specified element.
        """
        idx_set = self.m.get(val, set())
        idx_set.add(len(self.l))
        self.m[val] = idx_set
        self.l.append(val)
        return len(idx_set) == 1

    def remove(self, val: int) -> bool:
        """
        Removes a value from the collection. Returns true if the collection contained the specified element.
        """
        if val not in self.m:
            return False
        idx_set = self.m[val]
        idx = list(idx_set)[0]
        last_idx = len(self.l) - 1
        self.l[idx] = self.l[last_idx]
        idx_set.remove(idx)

        last_idx_set = self.m[self.l[last_idx]]
        if last_idx in last_idx_set:
            last_idx_set.remove(last_idx)
        if idx < last_idx:
            last_idx_set.add(idx)
        if not idx_set:
            self.m.pop(val)
        self.l.pop()
        return True

    def getRandom(self) -> int:
        """
        Get a random element from the collection.
        """
        return -1 if len(self.l) == 0 else random.choice(self.l)


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

Complexity

Measure	Complexity
Time	O(n)
Space	O(n) auxiliary

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 381. Insert Delete GetRandom O(1) - Duplicates allowed is filed here because LeetCode tags it Math, which is the vocabulary this hub collects.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 381. Insert Delete GetRandom O(1) - Duplicates allowed?: LeetCode 381. Insert Delete GetRandom O(1) - Duplicates allowed is rated Hard on LeetCode.
What is the time complexity of LeetCode 381. Insert Delete GetRandom O(1) - Duplicates allowed?: The Python solution on this page runs in O(n).
What is the space complexity of LeetCode 381. Insert Delete GetRandom O(1) - Duplicates allowed?: The Python solution on this page uses O(n) auxiliary space.
What topics does LeetCode 381. Insert Delete GetRandom O(1) - Duplicates allowed cover?: LeetCode 381. Insert Delete GetRandom O(1) - Duplicates allowed is tagged Design, Array, Hash Table, Math and Randomized on LeetCode.