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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()) // exist 12 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 exist 22 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 it 30 { 31 vit = array.erase(vit); 32 } 33 else 34 { 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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原文地址：http://www.cnblogs.com/ym65536/p/5935425.html
