380. Insert Delete GetRandom O(1)
Design a data structure that supports all following operations in average O(1) time.
insert(val)
: Inserts an item val to the set if not already present.remove(val)
: Removes an item val from the set if present.getRandom
: Returns a random element from current set of elements. Each element must have the same probability of being returned.
Example:
// Init an empty set. RandomizedSet randomSet = new RandomizedSet(); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomSet.insert(1); // Returns false as 2 does not exist in the set. randomSet.remove(2); // Inserts 2 to the set, returns true. Set now contains [1,2]. randomSet.insert(2); // getRandom should return either 1 or 2 randomly. randomSet.getRandom(); // Removes 1 from the set, returns true. Set now contains [2]. randomSet.remove(1); // 2 was already in the set, so return false. randomSet.insert(2); // Since 2 is the only number in the set, getRandom always return 2. randomSet.getRandom();
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();// move the last element to the deleted position 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: unordered_map<int,int>m; vector<int>nums; }; /** * 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(); */