103 lines
3.3 KiB
C++
103 lines
3.3 KiB
C++
// Source : https://leetcode.com/problems/insert-delete-getrandom-o1-duplicates-allowed/
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// Author : Hao Chen
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// Date : 2016-08-25
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/***************************************************************************************
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*
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* Design a data structure that supports all following operations in average O(1) time.
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* Note: Duplicate elements are allowed.
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*
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* insert(val): Inserts an item val to the collection.
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* remove(val): Removes an item val from the collection if present.
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* getRandom: Returns a random element from current collection of elements. The
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* probability of each element being returned is linearly related to the number of same
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* value the collection contains.
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*
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* Example:
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*
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* // Init an empty collection.
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* RandomizedCollection collection = new RandomizedCollection();
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*
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* // Inserts 1 to the collection. Returns true as the collection did not contain 1.
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* collection.insert(1);
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*
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* // Inserts another 1 to the collection. Returns false as the collection contained 1.
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* Collection now contains [1,1].
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* collection.insert(1);
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*
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* // Inserts 2 to the collection, returns true. Collection now contains [1,1,2].
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* collection.insert(2);
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*
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* // getRandom should return 1 with the probability 2/3, and returns 2 with the
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* probability 1/3.
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* collection.getRandom();
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*
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* // Removes 1 from the collection, returns true. Collection now contains [1,2].
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* collection.remove(1);
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*
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* // getRandom should return 1 and 2 both equally likely.
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* collection.getRandom();
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***************************************************************************************/
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class RandomizedCollection {
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public:
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/** Initialize your data structure here. */
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RandomizedCollection() {
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srand(time(NULL));
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}
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/** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */
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bool insert(int val) {
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data.push_back(val);
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valpos[val].insert( data.size() - 1 );
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return (valpos[val].size() == 1);
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}
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/** Removes a value from the collection. Returns true if the collection contained the specified element. */
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bool remove(int val) {
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// not found
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if (!find(val)) return false;
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//same idea with non-duplication version, but need be careful with some edge case
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int _idx = *(valpos[val].begin());
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int _val = data.back();
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valpos[_val].insert(_idx);
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data[_idx] = _val;
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valpos[val].erase(_idx);
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if (valpos[val].size()==0){
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valpos.erase(val);
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}
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data.pop_back();
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if ( _idx < data.size() ){
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valpos[_val].erase(data.size());
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valpos[_val].insert(_idx);
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}
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return true;
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}
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/** Get a random element from the collection. */
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int getRandom() {
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return data[ rand() % data.size() ];
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}
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private:
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unordered_map<int, unordered_set<int>> valpos; //value position map
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vector<int> data;
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bool find(int val) {
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return (valpos.find(val) != valpos.end());
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}
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};
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/**
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* Your RandomizedCollection object will be instantiated and called as such:
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* RandomizedCollection obj = new RandomizedCollection();
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* bool param_1 = obj.insert(val);
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* bool param_2 = obj.remove(val);
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* int param_3 = obj.getRandom();
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*/
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