Problem solution · C++

Insert Delete Getrandom O1 Duplicates Allowed

Insert Delete Getrandom O1 Duplicates Allowed: 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: 59 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 Duplicates Allowed, the implementation stores previously seen values or frequencies in a hash table for direct membership and lookup operations.

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

Code notes

59 lines of C++ from the credited upstream file insert-delete-getrandom-o1-duplicates-allowed.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 Duplicates Allowed · C++C++

Use this to learn the idea, then write your own version.

1// Time:  O(1)2// Space: O(n)3 4class RandomizedCollection {5public:6    /** Initialize your data structure here. */7    RandomizedCollection() : gen_(random_device()()) {8        9    }10    11    /** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */12    bool insert(int val) {13        bool has = used_.count(val);14 15        list_.emplace_back(val, used_[val].size());16        used_[val].emplace_back(list_.size() - 1);17 18        return !has; 19    }20    21    /** Removes a value from the collection. Returns true if the collection contained the specified element. */22    bool remove(int val) {23        if (!used_.count(val)) {24            return false;25        }26 27        used_[list_.back().first][list_.back().second] = used_[val].back();28        swap(list_[used_[val].back()], list_.back());29 30        used_[val].pop_back();31        if (used_[val].empty()) {32            used_.erase(val);33        }34        list_.pop_back();35 36        return true;  37    }38    39    /** Get a random element from the collection. */40    int getRandom() {41        uniform_int_distribution<int> dist(0, list_.size() - 1);42        return list_[dist(gen_)].first;43    }44 45private:46    vector<pair<int, int>> list_;47    unordered_map<int, vector<int>> used_;48    default_random_engine gen_;49};50 51/**52 * Your RandomizedCollection object will be instantiated and called as such:53 * RandomizedCollection obj = new RandomizedCollection();54 * bool param_1 = obj.insert(val);55 * bool param_2 = obj.remove(val);56 * int param_3 = obj.getRandom();57 */58 59

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Insert Delete Getrandom O1 Duplicates Allowed

Code notes

Complexity

Code and credit

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