pylist

657. Insert Delete GetRandom O(1)

Design a data structure that supports all following operations in average O(1) time.

• insert(val): Inserts an item val to the set if not already present.
• remove(val): Removes an item val from the set if present.
• getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.

Example

// Init an empty set.
RandomizedSet randomSet = new RandomizedSet();

// Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomSet.insert(1);

// Returns false as 2 does not exist in the set.
randomSet.remove(2);

// Inserts 2 to the set, returns true. Set now contains [1,2].
randomSet.insert(2);

// getRandom should return either 1 or 2 randomly.
randomSet.getRandom();

// Removes 1 from the set, returns true. Set now contains [2].
randomSet.remove(1);

// 2 was already in the set, so return false.
randomSet.insert(2);

// Since 2 is the only number in the set, getRandom always return 2.
randomSet.getRandom();

solution

class RandomizedSet:
    
    def __init__(self):
        self.set = set()
    """
    @param: val: a value to the set
    @return: true if the set did not already contain the specified element or false
    """
    def insert(self, val):
        if val in self.set:
            return False
        self.set.add(val)
        return True

    """
    @param: val: a value from the set
    @return: true if the set contained the specified element or false
    """
    def remove(self, val):
        if not val in self.set:
            return False
        self.set.remove(val)
        return True

    """
    @return: Get a random element from the set
    """
    def getRandom(self):
        out = self.set.pop()
        self.set.add(out)
        return out

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