99 lines
2.8 KiB
C++
99 lines
2.8 KiB
C++
// Source : https://leetcode.com/problems/insert-delete-getrandom-o1/
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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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*
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* insert(val): Inserts an item val to the set if not already present.
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* remove(val): Removes an item val from the set if present.
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* getRandom: Returns a random element from current set of elements. Each element must
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* have the same probability of being returned.
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*
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* Example:
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*
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* // Init an empty set.
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* RandomizedSet randomSet = new RandomizedSet();
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*
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* // Inserts 1 to the set. Returns true as 1 was inserted successfully.
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* randomSet.insert(1);
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*
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* // Returns false as 2 does not exist in the set.
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* randomSet.remove(2);
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*
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* // Inserts 2 to the set, returns true. Set now contains [1,2].
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* randomSet.insert(2);
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*
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* // getRandom should return either 1 or 2 randomly.
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* randomSet.getRandom();
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*
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* // Removes 1 from the set, returns true. Set now contains [2].
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* randomSet.remove(1);
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*
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* // 2 was already in the set, so return false.
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* randomSet.insert(2);
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*
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* // Since 1 is the only number in the set, getRandom always return 1.
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* randomSet.getRandom();
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***************************************************************************************/
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class RandomizedSet {
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public:
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/** Initialize your data structure here. */
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RandomizedSet() {
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srand(time(NULL));
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}
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/** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
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bool insert(int val) {
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if ( find(val) ) return false;
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data.push_back(val);
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valpos[val] = data.size() - 1;
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return true;
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}
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/** Removes a value from the set. Returns true if the set contained the specified element. */
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bool remove(int val) {
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if ( !find(val) ) return false;
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/*
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* Tricky
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* ------
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* 1) Copy the data from the last one to the place need be removed.
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* 2) Remove the last one.
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*/
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int _idx = valpos[val];
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int _val = data.back();
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data[_idx] = _val;
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valpos[_val] = _idx;
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valpos.erase(val);
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data.pop_back();
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return true;
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}
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/** Get a random element from the set. */
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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, 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 RandomizedSet object will be instantiated and called as such:
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* RandomizedSet obj = new RandomizedSet();
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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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