Problem
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 reporting a random element.
Implement the RandomizedCollection
class:
RandomizedCollection()
Initializes the emptyRandomizedCollection
object.bool insert(int val)
Inserts an itemval
into the multiset, even if the item is already present. Returnstrue
if the item is not present,false
otherwise.bool remove(int val)
Removes an itemval
from the multiset if present. Returnstrue
if the item is present,false
otherwise. Note that ifval
has 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 the 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 RandomizedCollection
.
Example 1:
Input
["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"]
[[], [1], [1], [2], [], [1], []]
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.
Constraints:
-231 <= val <= 231 - 1
At most
2 * 105
calls in total will be made toinsert
,remove
, andgetRandom
.There will be at least one element in the data structure when
getRandom
is called.
Solution
var RandomizedCollection = function() {
this.map = {};
this.arr = [];
};
/**
* @param {number} val
* @return {boolean}
*/
RandomizedCollection.prototype.insert = function(val) {
var notFound = this.map[val] === undefined;
if (notFound) this.map[val] = { arr: [], map: {} };
this.map[val].map[this.arr.length] = this.map[val].arr.length;
this.map[val].arr.push(this.arr.length);
this.arr.push(val);
return notFound;
};
/**
* @param {number} val
* @return {boolean}
*/
RandomizedCollection.prototype.remove = function(val) {
if (this.map[val] === undefined) return false;
var valIndexs = this.map[val].arr;
var delIndex = valIndexs[valIndexs.length - 1];
var lastValue = this.arr.pop();
if (valIndexs.length === 1) {
delete this.map[val];
} else {
valIndexs.pop();
delete this.map[val].map[delIndex];
}
if (lastValue !== val) {
var lastValueIndex = this.map[lastValue].map[this.arr.length];
this.map[lastValue].arr[lastValueIndex] = delIndex;
delete this.map[lastValue].map[this.arr.length];
this.map[lastValue].map[delIndex] = lastValueIndex;
this.arr[delIndex] = lastValue;
}
return true;
};
/**
* @return {number}
*/
RandomizedCollection.prototype.getRandom = function() {
var num = Math.floor(Math.random() * this.arr.length);
return this.arr[num];
};
/**
* Your RandomizedCollection object will be instantiated and called as such:
* var obj = new RandomizedCollection()
* var param_1 = obj.insert(val)
* var param_2 = obj.remove(val)
* var param_3 = obj.getRandom()
*/
Explain:
nope.
Complexity:
- Time complexity : O(1).
- Space complexity : O(n).