# [380\. Insert Delete GetRandom O(1)](https://leetcode.com/problems/insert-delete-getrandom-o1/)

:::spoiler Hint

class RandomizedSet {
private:
    // Map to store value and its index in the vector
    // Vector to store the values
    
public:
    RandomizedSet() {}
    
    bool insert(int val)
    {
        // If the value is already in the set, return false
        // Add the value to the end of the vector
        // Map the value to its index in the vector
        // Successfully inserted
    }
 
    bool remove(int val)
    {
        // If the value is not in the set, return false
        // Get the last element in the vector
        
        // Move the last element to the position of the element to be removed
        // Remove the last element from the vector
        
        // Erase the element from the map
        // Successfully removed
    }
    
    int getRandom()
    {
        // Return a random element from the vector
    }
};

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

:::

:::spoiler Solution

class RandomizedSet {
private:
    unordered_map<int, int> m;
    vector<int> nums;    
public:
    RandomizedSet() {}
    
    bool insert(int val)
    {
        if(m.count(val)) return false;
        
        nums.push_back(val);

        m[val] = nums.size() - 1;

        return true;
    }
 
    bool remove(int val)
    {
        if (!m.count(val)) return false;

        int lastElement = nums.back();
        
        nums[m[val]] = lastElement;
        m[lastElement] = m[val];

        nums.pop_back();
        m.erase(val);
        return true;        
    }
    
    int getRandom()
    {
        return nums[rand() % nums.size()];
    }
};

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

- Time Complexity: $O(1)$
- Space Complexity: $O(N)$
:::