【数组】380. 常数时间插入、删除和获取随机元素

 1 class RandomizedSet {
 2 public:
 3     /** Initialize your data structure here. */
 4     RandomizedSet() {
 5 
 6     }
 7     
 8     /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
 9     bool insert(int val) 
10     {
11         if (m.count(val)) 
12         {
13             return false;
14         }
15         nums.push_back(val);
16         m[val] = nums.size() - 1;
17         return true;
18 
19     }
20     
21     /** Removes a value from the set. Returns true if the set contained the specified element. */
22     bool remove(int val) {
23         if (!m.count(val)) 
24         {
25             return false;
26         }
27         int last = nums.back();
28         m[last] = m[val];
29         nums[m[val]] = last;
30         nums.pop_back();
31         m.erase(val);
32         return true;
33 
34     }
35     
36     /** Get a random element from the set. */
37     int getRandom() {
38         return nums[rand() % nums.size()];
39     }
40 
41 private:
42     vector<int> nums;
43     unordered_map<int, int> m;
44 
45 };