Last updated on January 5th, 2025 at 12:41 am

Here, we see an Insert Delete GetRandom O(1) LeetCode Solution. This Leetcode problem is solved using different approaches in many programming languages, such as C++, Java, JavaScript, Python, etc.

List of all LeetCode Solution

Topics

Array, Design, Hash Table

Companies

Amazon, Facebook, Google, Pocketgems, Twitter, Uber, Yelp

Level of Question

Medium

Insert Delete GetRandom O(1) LeetCode Solution

1. Problem Statement

Implement the RandomizedSet class:

• RandomizedSet() Initializes the RandomizedSet object.
• bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present, false otherwise.
• bool remove(int val) Removes an item val from the set if present. Returns true if the item was present, false otherwise.
• int getRandom() Returns a random element from the current set of elements (it’s guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned.

You must implement the functions of the class such that each function works in average O(1) time complexity.

Example 1:
Input [“RandomizedSet”, “insert”, “remove”, “insert”, “getRandom”, “remove”, “insert”, “getRandom”]
[[], [1], [2], [2], [], [1], [2], []]
Output [null, true, false, true, 2, true, false, 2]

Explanation
RandomizedSet randomizedSet = new RandomizedSet();
randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomizedSet.remove(2); // Returns false as 2 does not exist in the set.
randomizedSet.insert(2); // Inserts 2 to the set, returns true. Set now contains [1,2].
randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly.
randomizedSet.remove(1); // Removes 1 from the set, returns true. Set now contains [2].
randomizedSet.insert(2); // 2 was already in the set, so return false.
randomizedSet.getRandom(); // Since 2 is the only number in the set, getRandom() will always return 2.

2. Coding Pattern Used in Solution

The coding pattern used in this code is “Hashing with Array for Constant Time Operations”. The code leverages a combination of a hash map (or dictionary) and an array (or list) to achieve constant time complexity for insert, remove, and getRandom operations.

3. Code Implementation in Different Languages

3.1 Insert Delete GetRandom O(1) C++

class RandomizedSet {
private:
    vector<int> a;
    unordered_map<int,int> m;
public:
    RandomizedSet() {
    }
    
    bool insert(int val) {
        if(m.find(val)!=m.end())
            return false;
        else{
            a.push_back(val);
            m[val]=a.size()-1; 
            return true;
        }
    }
    
    bool remove(int val) {
        if(m.find(val)==m.end())
            return false;
        else{
            int last=a.back();
            a[m[val]]=a.back();
            a.pop_back();
            m[last]=m[val]; 
            m.erase(val);
            return true;
        }
    }
    
    int getRandom() {
        return a[rand()%a.size()];
    }
};

3.2 Insert Delete GetRandom O(1) Java

class RandomizedSet {
    private ArrayList<Integer> list;
    private Map<Integer, Integer> map;

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

    public boolean search(int val) {
        return map.containsKey(val);
    }

    public boolean insert(int val) {
        if (search(val)) return false;
        list.add(val);
        map.put(val, list.size() - 1);
        return true;
    }

    public boolean remove(int val) {
        if (!search(val)) return false;
        int index = map.get(val);
        list.set(index, list.get(list.size() - 1));
        map.put(list.get(index), index);
        list.remove(list.size() - 1);
        map.remove(val);
        return true;
    }

    public int getRandom() {
        Random rand = new Random();
        return list.get(rand.nextInt(list.size()));
    }
}

3.3 Insert Delete GetRandom O(1) JavaScript

var RandomizedSet = function() {
    this.set = [];
    this.valueIndexMap = new Map();
};

RandomizedSet.prototype.insert = function(val) {
    if (this.valueIndexMap.has(val)) {
        return false;
    }
    this.set.push(val);
    this.valueIndexMap.set(val, this.set.length -1);
    return true;
};

RandomizedSet.prototype.remove = function(val) {
    if (!this.valueIndexMap.has(val)) {
        return false;
    }
    const indexToRemove = this.valueIndexMap.get(val);
    this.valueIndexMap.set(this.set[this.set.length - 1], indexToRemove);
    this.valueIndexMap.delete(val);
    this.set[indexToRemove] = this.set[this.set.length - 1];
    this.set[this.set.length - 1] = val;
    this.set.pop();
    return true;
};

RandomizedSet.prototype.getRandom = function() {
    return this.set[Math.floor(Math.random()*this.set.length)];
}

3.4 Insert Delete GetRandom O(1) Python

class RandomizedSet(object):
    def __init__(self):
        self.lst = []
        self.idx_map = {}        
    def search(self, val):
        return val in self.idx_map

    def insert(self, val):
        if self.search(val):
            return False
        self.lst.append(val)
        self.idx_map[val] = len(self.lst) - 1
        return True

    def remove(self, val):
        if not self.search(val):
            return False
        idx = self.idx_map[val]
        self.lst[idx] = self.lst[-1]
        self.idx_map[self.lst[-1]] = idx
        self.lst.pop()
        del self.idx_map[val]
        return True

    def getRandom(self):
        return random.choice(self.lst)

4. Time and Space Complexity

	Time Complexity	Space Complexity
C++	O(1)	O(n)
Java	O(1)	O(n)
JavaScript	O(1)	O(n)
Python	O(1)	O(n)

where, n is the number of elements in the set.