# LeetCode Insert Delete GetRandom O(1) - Duplicates allowed

LeetCode Insert Delete GetRandom O(1) - 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.

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();```

```class RandomizedCollection {
private:
unordered_map<int, priority_queue<int>> hash;
vector<int> nums;
public:
/** Initialize your data structure here. */
RandomizedCollection() {

}

/** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */
bool insert(int val) {
hash[val].push(nums.size());
nums.push_back(val);
return hash[val].size() == 1;
}

/** Removes a value from the collection. Returns true if the collection contained the specified element. */
bool remove(int val) {
if (hash[val].empty())return false;
int pos = hash[val].top();
hash[val].pop();
if (pos != nums.size() - 1) {
nums[pos] = nums[nums.size() - 1];
hash[nums[pos]].pop();
hash[nums[pos]].push(pos);
}
nums.pop_back();
return true;
}

/** Get a random element from the collection. */
int getRandom() {
return nums[rand() % nums.size()];
}
};
```

• 10:[0,1]
• 20:[2,3]
• 30:[4,5]

• 10:[0]
• 20:[2,3]
• 30:[4,1]

• 10:[]
• 20:[2,3]
• 30:[4,0]

```class RandomizedCollection {
private:
unordered_map<int, unordered_set<int>> hash;
vector<int> nums;
public:
/** Initialize your data structure here. */
RandomizedCollection() {

}

/** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */
bool insert(int val) {
hash[val].insert(nums.size());
nums.push_back(val);
return hash[val].size() == 1;
}

/** Removes a value from the collection. Returns true if the collection contained the specified element. */
bool remove(int val) {
if (hash[val].empty())return false;
int pos = *hash[val].begin();
hash[val].erase(pos);
if (pos != nums.size() - 1) {
nums[pos] = nums[nums.size() - 1];
hash[nums[pos]].erase(nums.size() - 1);
hash[nums[pos]].insert(pos);
}
nums.pop_back();
return true;
}

/** Get a random element from the collection. */
int getRandom() {
return nums[rand() % nums.size()];
}
};
```