Insert Delete GetRandom O(1) – LeetCode Solution Java , Python 3, Python 2 , C , C++, Best and Optimal Solutions , All you need.

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.

Constraints:

• -231 <= val <= 231 - 1
• At most 2 * 105 calls will be made to insert, remove, and getRandom.
• There will be at least one element in the data structure when getRandom is called.

C++ Insert Delete GetRandom O(1) LeetCode Solution

class RandomizedSet {
public:
    /** Initialize your data structure here. */
    RandomizedSet() {
        
    }
    
    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    bool insert(int val) {
        if (m.find(val) != m.end()) return false;
        nums.emplace_back(val);
        m[val] = nums.size() - 1;
        return true;
    }
    
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    bool remove(int val) {
        if (m.find(val) == m.end()) return false;
        int last = nums.back();
        m[last] = m[val];
        nums[m[val]] = last;
        nums.pop_back();
        m.erase(val);
        return true;
    }
    
    /** Get a random element from the set. */
    int getRandom() {
        return nums[rand() % nums.size()];
    }
private:
    vector<int> nums;
    unordered_map<int, int> m;
};

Java Insert Delete GetRandom O(1) LeetCode Solution

public class RandomizedSet {

    HashMap<Integer, Integer> valToInd;
    List<Integer> list;
    int ind = 0;
    
    /** Initialize your data structure here. */
    public RandomizedSet() {
        valToInd = new HashMap<>();
        list = new ArrayList<>();
    }
    
    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    public boolean insert(int val) {
        if(valToInd.containsKey(val)) return false;
        list.add(val);
        valToInd.put(val,list.size()-1);
        return true;
    }
    
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    public boolean remove(int val) {
        int ind = valToInd.getOrDefault(val,-1);
        if(ind == -1) return false;
        Collections.swap(list,ind,list.size()-1);
        int swappedWith = list.get(ind);
        valToInd.put(swappedWith,ind);
        list.remove(list.size()-1);
        valToInd.remove(val);
        return true;
    }
    
    /** Get a random element from the set. */
    public int getRandom() {
        int max = list.size();
        int min = 0;
        int ind = (int)(Math.random() * (max - min) + min);
        return list.get(ind);
    }
}
 

Python 3 Insert Delete GetRandom O(1) LeetCode Solution

import random

class RandomizedSet(object):

    def __init__(self):
        self.nums, self.pos = [], {}
        
    def insert(self, val):
        if val not in self.pos:
            self.nums.append(val)
            self.pos[val] = len(self.nums) - 1
            return True
        return False
        

    def remove(self, val):
        if val in self.pos:
            idx, last = self.pos[val], self.nums[-1]
            self.nums[idx], self.pos[last] = last, idx
            self.nums.pop(); self.pos.pop(val, 0)
            return True
        return False
            
    def getRandom(self):
        return self.nums[random.randint(0, len(self.nums) - 1)]

Array-1180
String-562
Hash Table-412
Dynamic Programming-390
Math-368
Sorting-264

Greedy-257
Depth-First Search-256
Database-215
Breadth-First Search-200
Tree-195

Binary Search-191
Matrix-176
Binary Tree-160
Two Pointers-151
Bit Manipulation-140

Stack-133
Heap (Priority Queue)-117
Design-116
Graph-108
Simulation-103
Prefix Sum-96

Backtracking-92
Counting-86
Sliding Window-73
Linked List-69
Union Find-66

Ordered Set-48
Monotonic Stack-47
Recursion-43
Trie-41
Binary Search Tree-40
Divide and Conquer-40

Enumeration-39
Bitmask-37
Queue-33
Memoization-32
Topological Sort-31

Geometry-30
Segment Tree-27
Game Theory-24
Hash Function-24
Binary Indexed Tree-21

Interactive-18
Data Stream-17
String Matching-17
Rolling Hash-17
Shortest Path-16

Number Theory-16
Combinatorics-15
Randomized-12
Monotonic Queue-9
Iterator-9
Merge Sort-9

Concurrency-9
Doubly-Linked List-8
Brainteaser-8
Probability and Statistics-7
Quickselect-7

Bucket Sort-6
Suffix Array-6
Minimum Spanning Tree-5
Counting Sort-5
Shell-4

Line Sweep-4
Reservoir Sampling-4
Eulerian Circuit-3
Radix Sort-3

Strongly Connected Componen-t2
Rejection Sampling-2
Biconnected Component-1

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