Written by Ron on 010111 April 000112011. Posted in Blog

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.

import random

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

    def insert(self, val: int) -> bool:
        if val in self.dict:
            return False
        else:
            self.dict[val] = len(self.list)
            self.list.append(val)
            return True
        
    def remove(self, val: int) -> bool:
        if val in self.dict:
            last_element, idx = self.list[-1], self.dict[val]
            self.list[idx], self.dict[last_element] = last_element, idx
            
            self.list.pop()
            del self.dict[val]
            return True
        else:
            return False
        
    def getRandom(self) -> int:
        return random.choice(self.list)

class RandomizedSet:

    def __init__(self):
        self.list = set()
        
    def insert(self, val: int) -> bool:
        if val not in self.list:
            self.list.add(val)
            return True
        else:
            return False
            
    def remove(self, val: int) -> bool:
        try:
            self.list.remove(val)
            return True
        except:
            return False
            
    def getRandom(self) -> int:
        return random.sample(self.list, 1) [0]


obj = RandomizedSet()
print(obj.insert(10))#true
print(obj.remove(20))#false
print(obj.insert(20))#true
print(obj.getRandom())# 10 or 20
print(obj.remove(10))#true
print(obj.insert(20))#false
print(obj.getRandom())# 20