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Insert Delete GetRandom O(1)

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Description

https://leetcode.com/problems/insert-delete-getrandom-o1/description/

Solution

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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(this->hash.find(val) != this->hash.end()) return false;
        this->hash[val] = this->nums.size();
        this->nums.push_back(val);
        return true;
    }
    
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    bool remove(int val) {
        auto iter = this->hash.find(val);
        if(iter == this->hash.end()) return false;
        int originIndex = iter->second;
        this->swap(nums, originIndex, this->nums.size() - 1);
        this->hash[this->nums[originIndex]] = originIndex;
        this->nums.pop_back();
        this->hash.erase(val);
        return true;
    }
    
    void swap(vector<int>& nums, int left, int right) {
        int temp = nums[left];
        nums[left] = nums[right];
        nums[right] = temp;
    }
    
    /** Get a random element from the set. */
    int getRandom() {
        if (this->nums.size() == 0) return -1;
        return this->nums[rand() % (this->nums.size())];
    }
    
private:
    unordered_map<int, int> hash;
    vector<int> nums;
};

/**
 * 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();
 */