> ## 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) Python Solution

> Tested Python solution for LeetCode 380 with 15 pytest cases. Generate a practice environment with lcpy.

LeetCode 380, Medium. Topics: Array, Hash Table, Math, Design. [View on LeetCode](https://leetcode.com/problems/insert-delete-getrandom-o1/description/).

Generate this problem as a practice environment: tested reference solution, 15 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 380   # by problem number
lcpy gen -s insert_delete_getrandom_o1   # by problem name
```

## Problem

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.

### Examples

```
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.

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/insert_delete_getrandom_o1/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/insert_delete_getrandom_o1/test_solution.py):

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


class RandomizedSet:
    # List stores values; dict maps value -> index in list.
    # O(1) remove via swap-with-last trick: move last element into removed slot.
    # Time: O(1) average per operation
    # Space: O(n)
    def __init__(self) -> None:
        self.values: list[int] = []
        self.index: dict[int, int] = {}

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

    def remove(self, val: int) -> bool:
        if val not in self.index:
            return False
        last_val = self.values[-1]
        remove_idx = self.index[val]
        # Move last element into the removed slot, then drop the tail
        self.values[remove_idx] = last_val
        self.index[last_val] = remove_idx
        self.values.pop()
        del self.index[val]
        return True

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

## Complexity

| Time                       | Space |
| -------------------------- | ----- |
| O(1) average per operation | O(n)  |

## Tags

[Grind](/catalog/grind), [NeetCode All](/catalog/neetcode).