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Problem solution · C++

Insert Delete Getrandom O1

Insert Delete Getrandom O1: a C++ solution using hash-based lookup. Learn the idea, check the complexity, and read the full code, with credit to Kamyu LeetCode Solutions.

Technique
Hash-based lookup
Source
Kamyu LeetCode Solutions
Length
58 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Hash-based lookup

For Insert Delete Getrandom O1, the implementation stores previously seen values or frequencies in a hash table for direct membership and lookup operations.

  1. Decide the key that represents the information needed later.
  2. Update its count or stored state while scanning the input.
  3. Use constant-time expected lookups to detect matches or assemble the result.

Code notes

  • 58 lines of C++ from the credited upstream file insert-delete-getrandom-o1.cpp.
  • The implementation visibly relies on sequence storage, hash lookup.
  • No explicit loop blocks detected.

Complexity

Expected hash operations are constant time, but the surrounding scan and the number of stored keys determine total work and memory.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from Kamyu LeetCode Solutions by kamyu104 and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeInsert Delete Getrandom O1 · C++C++
Use this to learn the idea, then write your own version.
// Time:  O(1)// Space: O(n) class RandomizedSet {public:    /** Initialize your data structure here. */    RandomizedSet() : gen_(random_device()()) {            }        /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */    bool insert(int val) {        if (used_.count(val)) {            return false;        }         set_.emplace_back(val);        used_[val] = set_.size() - 1;         return true;    }        /** Removes a value from the set. Returns true if the set contained the specified element. */    bool remove(int val) {        if (!used_.count(val)) {            return false;        }         used_[set_.back()] = used_[val];        swap(set_[used_[val]], set_.back());         used_.erase(val);        set_.pop_back();         return true;    }        /** Get a random element from the set. */    int getRandom() {        uniform_int_distribution<int> dist(0, set_.size() - 1);        return set_[dist(gen_)];    } private:    vector<int> set_;    unordered_map<int, int> used_;    default_random_engine gen_;}; /** * 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(); */

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