# Leetcode 381 Solution

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

## Solution

``````class RandomizedCollection {
map<int, list<int>> m_m;
vector<pair<int, int*>> m_v;

public:
/** Initialize your data structure here. */
RandomizedCollection() {

}

void display()
{
for (auto pair : m_m)
{
printf("%d: ", pair.first);
for (auto val : pair.second)
printf("%d ", val);
printf("\n");
}
for (auto pair : m_v)
printf("%d ", pair.first);
printf("\n\n\n");
}

/** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */
bool insert(int val) {
bool res = false;

if (m_m.find(val) == m_m.end())
{
m_m[val] = list<int>();
res = true;
}

m_m[val].push_back(m_v.size());
m_v.push_back(make_pair(val, (int*)&m_m[val].back()));

return res;
}

/** Removes a value from the collection. Returns true if the collection contained the specified element. */
bool remove(int val) {
if (m_m.find(val) == m_m.end())
return false;

int index = *m_m[val].rbegin();
swap(m_v[index], m_v[m_v.size() - 1]);

m_v.pop_back();
m_m[val].pop_back();
if (m_m[val].empty())
m_m.erase(val);

*m_v[index].second = index;

return true;
}

/** Get a random element from the collection. */
int getRandom() {
int index = rand() % m_v.size();
return m_v[index].first;
}
};

/**
* 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();
*/
``````