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randomized_set.py
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"""
Randomized Set
A data structure that supports insert, remove, and get-random-element
operations, all in average O(1) time.
Reference: https://leetcode.com/problems/insert-delete-getrandom-o1/
Complexity:
Time: O(1) average for insert, remove, and random_element
Space: O(n)
"""
from __future__ import annotations
import random
class RandomizedSet:
"""A set supporting O(1) insert, remove, and random access."""
def __init__(self) -> None:
self.elements: list[int] = []
self.index_map: dict[int, int] = {}
def insert(self, new_one: int) -> None:
"""Insert a value into the set if not already present.
Args:
new_one: The value to insert.
"""
if new_one in self.index_map:
return
self.index_map[new_one] = len(self.elements)
self.elements.append(new_one)
def remove(self, old_one: int) -> None:
"""Remove a value from the set if present.
Args:
old_one: The value to remove.
"""
if old_one not in self.index_map:
return
index = self.index_map[old_one]
last = self.elements.pop()
self.index_map.pop(old_one)
if index == len(self.elements):
return
self.elements[index] = last
self.index_map[last] = index
def random_element(self) -> int:
"""Return a random element from the set.
Returns:
A randomly chosen element.
"""
return random.choice(self.elements)