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[leetcode] 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 1 is the only number in the set, getRandom always return 1.randomSet.getRandom();
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Solution:
1 class RandomizedSet { 2 public: 3 /** Initialize your data structure here. */ 4 RandomizedSet() 5 { 6 } 7 8 /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */ 9 bool insert(int val) 10 {11 if (hset.find(val) != hset.end()) // exist12 return false;13 hset.insert(val);14 array.push_back(val);15 return true;16 }17 18 /** Removes a value from the set. Returns true if the set contained the specified element. */19 bool remove(int val) 20 {21 if (hset.find(val) == hset.end()) // not exist22 return false;23 unordered_set<int>::iterator sit = hset.find(val);24 hset.erase(sit);25 26 vector<int>::iterator vit = array.begin();27 while (vit != array.end())28 {29 if (*vit == val) // erase it30 {31 vit = array.erase(vit);32 }33 else34 {35 vit++;36 }37 }38 39 return true;40 }41 42 /** Get a random element from the set. */43 int getRandom() 44 {45 return array[rand() % array.size()];46 }47 48 private:49 vector<int> array;50 unordered_set<int> hset;51 };
[leetcode] 380. Insert Delete GetRandom O(1)
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