> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Insert Delete GetRandom O(1) - Duplicates

> Tested Python solution for LeetCode 381 with 20 pytest cases. Generate a practice environment with lcpy.

LeetCode 381, [Hard](/catalog/hard). Topics: [Array](/catalog/topics/array), [Hash Table](/catalog/topics/hash-table), [Math](/catalog/topics/math), [Design](/catalog/topics/design), Randomized. [View on LeetCode](https://leetcode.com/problems/insert-delete-getrandom-o1-duplicates-allowed/description/).

Generate this problem as a practice environment: tested reference solution, 20 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 381   # by problem number
lcpy gen -s insert_delete_getrandom_o1_duplicates_allowed   # by problem name
```

## 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.

Implement the `RandomizedCollection` class:

* `RandomizedCollection()` Initializes the empty `RandomizedCollection` object.
* `bool insert(int val)` Inserts an item `val` into the multiset, even if the item is already present. Returns `true` if the item is not present, `false` otherwise.
* `bool remove(int val)` Removes an item `val` from the multiset if present. Returns `true` if the item is present, `false` otherwise. Note that if `val` has multiple occurrences in the multiset, we only remove one of them.
* `int getRandom()` Returns a random element from the current multiset of elements. The probability of each element being returned is **linearly related** to the number of the same values the multiset contains.

You must implement the functions of the class such that each function works on **average** `O(1)` time complexity.

**Note:** The test cases are generated such that `getRandom` will only be called if there is at least one item in the `RandomizedCollection`.

### Examples

```
Input
["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"]
[[], [1], [1], [2], [], [1], []]
Output
[null, true, false, true, 2, true, 1]

Explanation
RandomizedCollection randomizedCollection = new RandomizedCollection();
randomizedCollection.insert(1);   // return true since the collection does not contain 1.
                                  // Inserts 1 into the collection.
randomizedCollection.insert(1);   // return false since the collection contains 1.
                                  // Inserts another 1 into the collection. Collection now contains [1,1].
randomizedCollection.insert(2);   // return true since the collection does not contain 2.
                                  // Inserts 2 into the collection. Collection now contains [1,1,2].
randomizedCollection.getRandom(); // getRandom should:
                                  // - return 1 with probability 2/3, or
                                  // - return 2 with probability 1/3.
randomizedCollection.remove(1);   // return true since the collection contains 1.
                                  // Removes 1 from the collection. Collection now contains [1,2].
randomizedCollection.getRandom(); // getRandom should return 1 or 2, both equally likely.
```

### Constraints

* `-2^31 <= val <= 2^31 - 1`
* At most `2 * 10^5` calls in total will be made to `insert`, `remove`, and `getRandom`.
* There will be **at least one** element in the data structure when `getRandom` is called.

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/insert_delete_getrandom_o1_duplicates_allowed/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/insert_delete_getrandom_o1_duplicates_allowed/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
import random


class RandomizedCollection:
    # Time: insert O(1), remove O(1), get_random O(1) average
    # Space: O(n)
    def __init__(self) -> None:
        self.vals: list[int] = []
        self.positions: dict[int, set[int]] = {}

    def insert(self, val: int) -> bool:
        self.vals.append(val)
        self.positions.setdefault(val, set()).add(len(self.vals) - 1)
        return len(self.positions[val]) == 1

    def remove(self, val: int) -> bool:
        indices = self.positions.get(val)
        if not indices:
            return False
        idx = indices.pop()
        last = len(self.vals) - 1
        last_val = self.vals[last]
        self.vals[idx] = last_val
        self.positions[last_val].add(idx)
        self.positions[last_val].discard(last)
        self.vals.pop()
        if not self.positions[val]:
            del self.positions[val]
        return True

    def get_random(self) -> int:
        return random.choice(self.vals)
```

## Complexity

| Time | Space |
| - | - |
| insert O(1), remove O(1), get\_random O(1) average | O(n) |

## Tags


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