0380-insert-delete-getrandom-o1.py

# https://leetcode.com/problems/insert-delete-getrandom-o1/submissions/
# O(1) - Time
# O(n) - Space

# Idea:
# Keep nums array and pos hashmap
# When adding append to end and add index to hashmap
# When removing swap the val with last item
# Pop the last item

from random import randint

class RandomizedSet:

    
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.nums = []
        self.pos = {}

    def insert(self, val: int) -> bool:
        """
        Inserts a value to the set. Returns true if the set did not already contain the specified element.
        """
        if val not in self.nums:
            self.nums.append(val)
            self.pos[val] = len(self.nums)-1
            return True
        return False
        

    def remove(self, val: int) -> bool:
        """
        Removes a value from the set. Returns true if the set contained the specified element.
        """
        if val in self.nums:
            last = self.nums[-1]
            idx = self.pos[val]
            
            self.pos[last] = idx
            self.nums[idx] = last
            
            self.nums.pop()
            del self.pos[val]
            
            return True
        return False

    def getRandom(self) -> int:
        """
        Get a random element from the set.
        """
        return self.nums[randint(0, len(self.nums)-1)]


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