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

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

class RandomizedCollection {
public:
    /** Initialize your data structure here. */
    unordered_map<int, unordered_set<int>> idx;
    vector<int> vals;
    
    RandomizedCollection() {
        
    }
    
    /** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */
    bool insert(int val) {
        idx[val].insert(vals.size());
        vals.push_back(val);
        return idx[val].size() == 1;
    }
    
    /** Removes a value from the collection. Returns true if the collection contained the specified element. */
    bool remove(int val) {
        if (!idx[val].empty()) {
            int index = *idx[val].begin();
            idx[val].erase(index);
            idx[vals.back()].erase(vals.size() - 1);
            if (index != vals.size() - 1) {
                idx[vals.back()].insert(index);
                swap(vals[index], vals[vals.size() - 1]);
            }
            vals.pop_back();
            return true;
        }
        return false;
    }
    
    /** Get a random element from the collection. */
    int getRandom() {
        return vals[rand() % vals.size()];
    }
};

/**
 * Your RandomizedCollection object will be instantiated and called as such:
 * RandomizedCollection* obj = new RandomizedCollection();
 * bool param_1 = obj->insert(val);
 * bool param_2 = obj->remove(val);
 * int param_3 = obj->getRandom();
 */