# 380 - Insert Delete GetRandom O(1)
解法一 - Hash Table + Array
這題是擴展眼界題,邊聽影片邊做,可以看:https://www.youtube.com/watch?v=y240Qh9H9uk
class RandomizedSet {
public:
/** Initialize your data structure here. */
RandomizedSet() {
}
/** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
bool insert(int val) {
// If the value is inside m_, return false
if(m_.count(val)) { return false; }
// If not exist, append to the back of array and record in the m_
m_[val] = vals_.size();
vals_.push_back(val);
return true;
}
/** Removes a value from the set. Returns true if the set contained the specified element. */
bool remove(int val) {
// If the value is not inside m_, return false
if(!m_.count(val)) { return false; }
// If exist, append to the back of array and remove from m_
int index = m_[val];
m_[vals_.back()] = index;
m_.erase(val);
swap(vals_[index], vals_.back());
vals_.pop_back();
return true;
}
/** Get a random element from the set. */
int getRandom() {
int index = rand() % vals_.size();
return vals_[index];
}
private:
unordered_map<int, int> m_; // stores value and array index
vector<int> vals_; // stores the value for getRandom
};
/**
* Your RandomizedSet object will be instantiated and called as such:
* RandomizedSet* obj = new RandomizedSet();
* bool param_1 = obj->insert(val);
* bool param_2 = obj->remove(val);
* int param_3 = obj->getRandom();
*/
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