RandomizedCollection is a data structure that contains a collection of numbers, possibly duplicates (i.e., a multiset). It should support inserting and removing specific elements and also removing a random element.
RandomizedCollection()Initializes the empty RandomizedCollection object.
bool insert(int val)Inserts an item
valinto the multiset, even if the item is already present. Returns
trueif the item is not present,
bool remove(int val)Removes an item
valfrom the multiset if present. Returns
trueif the item is present,
falseotherwise. Note that if
valhas multiple occurrences in the multiset, we only remove one of them.
int getRandom()Returns a random element from the current multiset of elements. The probability of each element being returned is linearly related to the number of same values the multiset contains.
You must implement the functions of the class such that each function works on average
O(1) time complexity.
Note: The test cases are generated such that
getRandom will only be called if there is at least one item in the
Input ["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"] [, , , , , , ] Output [null, true, false, true, 2, true, 1] Explanation RandomizedCollection randomizedCollection = new RandomizedCollection(); randomizedCollection.insert(1); // return true since the collection does not contain 1. // Inserts 1 into the collection. randomizedCollection.insert(1); // return false since the collection contains 1. // Inserts another 1 into the collection. Collection now contains [1,1]. randomizedCollection.insert(2); // return true since the collection does not contain 2. // Inserts 2 into the collection. Collection now contains [1,1,2]. randomizedCollection.getRandom(); // getRandom should: // - return 1 with probability 2/3, or // - return 2 with probability 1/3. randomizedCollection.remove(1); // return true since the collection contains 1. // Removes 1 from the collection. Collection now contains [1,2]. randomizedCollection.getRandom(); // getRandom should return 1 or 2, both equally likely.
-231 <= val <= 231 - 1
- At most
2 * 105calls in total will be made to
- There will be at least one element in the data structure when
Use an array to record all numbers and for selecting one randomly,
and a dictionary of set for getting the index of a number.