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day-73.cpp
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day-73.cpp
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/*
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.
*/
// Average O(1) implementation with vector and map
class RandomizedSet {
public:
/** Initialize your data structure here. */
unordered_map<int, int> hashMap;
vector<int> customSet;
RandomizedSet() {
hashMap = unordered_map<int, int>();
customSet = vector<int>();
}
/** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
bool insert(int val) {
if (hashMap.count(val) > 0) return false;
customSet.push_back(val);
hashMap[val] = customSet.size() - 1;
return true;
}
/** Removes a value from the set. Returns true if the set contained the specified element. */
bool remove(int val) {
if (hashMap.count(val) == 0) return false;
int idx = hashMap[val];
hashMap[customSet.back()] = idx;
hashMap.erase(val);
swap(customSet[idx], customSet.back());
customSet.pop_back();
return true;
}
/** Get a random element from the set. */
int getRandom() {
return customSet[rand() % customSet.size()];
}
};