381. Insert Delete GetRandom O(1) - Duplicates allowed

  • 28.4%

https://leetcode.com/problems/insert-delete-getrandom-o1-duplicates-allowed/

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

Note: Duplicate elements are allowed.

  1. insert(val): Inserts an item val to the collection.
  2. remove(val): Removes an item val from the collection if present.
  3. getRandom: Returns a random element from current collection of elements. The probability of each element being returned is linearly related to the number of same value the collection contains.
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> Example:
>
> // Init an empty collection.
> RandomizedCollection collection = new RandomizedCollection();
>
> // Inserts 1 to the collection. Returns true as the collection did not contain 1.
> collection.insert(1);
>
> // Inserts another 1 to the collection. Returns false as the collection contained 1. Collection now contains [1,1].
> collection.insert(1);
>
> // Inserts 2 to the collection, returns true. Collection now contains [1,1,2].
> collection.insert(2);
>
> // getRandom should return 1 with the probability 2/3, and returns 2 with the probability 1/3.
> collection.getRandom();
>
> // Removes 1 from the collection, returns true. Collection now contains [1,2].
> collection.remove(1);
>
> // getRandom should return 1 and 2 both equally likely.
> collection.getRandom();
>

python

238ms, September 12, 2016

https://discuss.leetcode.com/topic/53896/frugal-python-code

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class RandomizedCollection(object):

def __init__(self):
"""
Initialize your data structure here.
"""
self.vals, self.idxs = [], collections.defaultdict(set)


def insert(self, val):
"""
Inserts a value to the collection. Returns true if the collection did not already contain the specified element.
:type val: int
:rtype: bool
"""
self.vals.append(val)
self.idxs[val].add(len(self.vals)-1)
return len(self.idxs[val]) == 1

def remove(self, val):
"""
Removes a value from the collection. Returns true if the collection contained the specified element.
:type val: int
:rtype: bool
"""
if self.idxs[val]:
out, ins = self.idxs[val].pop(), self.vals[-1]
self.vals[out] = ins
if self.idxs[ins]:
self.idxs[ins].add(out)
self.idxs[ins].discard(len(self.vals)-1)
self.vals.pop()
return True
return False


def getRandom(self):
"""
Get a random element from the collection.
:rtype: int
"""
return random.choice(self.vals)



# Your RandomizedCollection object will be instantiated and called as such:
# obj = RandomizedCollection()
# param_1 = obj.insert(val)
# param_2 = obj.remove(val)
# param_3 = obj.getRandom()
谢谢你,可爱的朋友。