## Algorithm

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

`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.

Implement the `RandomizedCollection` class:

• `RandomizedCollection()` Initializes the empty `RandomizedCollection` object.
• `bool insert(int val)` Inserts an item `val` into the multiset, even if the item is already present. Returns `true` if the item is not present, `false` otherwise.
• `bool remove(int val)` Removes an item `val` from the multiset if present. Returns `true` if the item is present, `false` otherwise. Note that if `val` 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 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 to `insert`, `remove`, and `getRandom`.
• There will be at least one element in the data structure when `getRandom` is called.

## Code Examples

### #1 Code Example with Java Programming

```Code - Java Programming```

``````
class RandomizedCollection {

Map> map;
List list;

public RandomizedCollection() {
map = new HashMap<>();
list = new ArrayList<>();
}

public boolean insert(int val) {
return map.get(val).size() == 1;
}

public boolean remove(int val) {
if (!map.containsKey(val) || map.get(val).size() == 0) {
return false;
}

int idxToRemove = map.get(val).iterator().next();
map.get(val).remove(idxToRemove);
int lastVal = list.get(list.size() - 1);
list.set(idxToRemove, lastVal);
map.get(lastVal).remove(list.size() - 1);
list.remove(list.size() - 1);

return true;
}

public int getRandom() {
return list.get(new java.util.Random().nextInt(list.size()));
}
}
``````
Copy The Code &

Input

cmd
["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"] [[], [1], [1], [2], [], [1], []]

Output

cmd
[null, true, false, true, 2, true, 1]

### #2 Code Example with Javascript Programming

```Code - Javascript Programming```

``````
const RandomizedCollection = function() {
this.map = new Map()
this.list = []
}

RandomizedCollection.prototype.insert = function(val) {
const index = this.list.length
const node = { val, index }
this.list[index] = node

const nodeList = this.map.get(val)
const isNew = nodeList === undefined || nodeList.length === 0
if (nodeList === undefined) {
this.map.set(val, [node])
} else {
nodeList.push(node)
}
return isNew
}

RandomizedCollection.prototype.remove = function(val) {
const nodeList = this.map.get(val)
if (!nodeList || nodeList.length === 0) return false
const node = nodeList.pop()
const replacement = this.list.pop()
if (replacement.index !== node.index) {
replacement.index = node.index
this.list[replacement.index] = replacement
}
return true
}

RandomizedCollection.prototype.getRandom = function() {
const index = Math.floor(Math.random() * this.list.length)
return this.list[index].val
}
``````
Copy The Code &

Input

cmd
["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"] [[], [1], [1], [2], [], [1], []]

Output

cmd
[null, true, false, true, 2, true, 1]

### #3 Code Example with Python Programming

```Code - Python Programming```

``````
class RandomizedCollection:

def __init__(self):
self.arr, self.pos = [], collections.defaultdict(set)
def insert(self, val):
out = val not in self.pos
self.arr.append(val)
return out

def remove(self, val):
if val in self.pos:
if self.arr[-1] != val:
x, y = self.pos[val].pop(), self.arr[-1]
self.arr[x] = y
else:
self.arr.pop()
if not self.pos[val]:
self.pos.pop(val)
return True
return False

def getRandom(self):
return random.choice(self.arr)
``````
Copy The Code &

Input

cmd
["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"] [[], [1], [1], [2], [], [1], []]

Output

cmd
[null, true, false, true, 2, true, 1]

### #4 Code Example with Python Programming

```Code - Python Programming```

``````
using System;
using System.Collections.Generic;
using System.Linq;

namespace LeetCode
{
public class _0381_InsertDeleteGetrandomDuplicatesAllowed
{

public _0381_InsertDeleteGetrandomDuplicatesAllowed()
{
random = new Random();
locations = new Dictionary>();
nums = new List();
}

public bool Insert(int val)
{
if (!locations.ContainsKey(val))
locations[val] = new HashSet();

return locations[val].Count == 1;
}

public bool Remove(int val)
{
if (!locations.ContainsKey(val)) return false;

var id = locations[val].First();
locations[val].Remove(id);

var num = nums[nums.Count - 1];
nums[id] = num;
locations[num].Remove(nums.Count - 1);
nums.RemoveAt(nums.Count - 1);

if (locations[val].Count == 0) locations.Remove(val);

return true;
}

/** Get a random element from the collection. */
public int GetRandom()
{
var id = random.Next(nums.Count);
return nums[id];
}
}

}
``````
Copy The Code &

Input

cmd
["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"] [[], [1], [1], [2], [], [1], []]

Output

cmd
[null, true, false, true, 2, true, 1]