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380. Insert Delete GetRandom O(1) #249

Open huimeich opened 5 years ago

huimeich commented 5 years ago

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();

huimeich commented 5 years ago 
def __init__(self):
    """
    Initialize your data structure here.
    """
    self.stack = []
    self.idict = {}

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 in self.idict:
        return False
    self.stack.append(val)
    self.idict[val] = len(self.stack) - 1
    return True

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.idict:
        i = self.idict[val]
        del self.idict[val]
        if i != len(self.stack) - 1:
            self.stack[i] = self.stack[-1]
            self.idict[self.stack[i]] = i
        self.stack.pop()
        return True
    return False

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