[Google] 出现次数最多的前K个元素

interface TopN {
　　void insert(String query);
　　List<String> getTop(int n);
}

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 
 4 class TopK {
 5     private:
 6         struct node {
 7             string id;
 8             int cnt;
 9             node(string _id, int _cnt) : id(_id), cnt(_cnt) {}
10         };
11 
12         unordered_map<string, int> mp;
13         vector<node> v;
14 
15     public:
16         void insert(string s) {
17             if (mp.find(s) == mp.end()) {
18                 v.push_back(node(s, 1));
19                 int idx = v.size() - 1;
20                 mp[s] = idx;
21             } else {
22                 int idx = mp[s], j;
23                 ++v[idx].cnt;
24                 node tmp = v[idx];
25                 for (j = idx - 1; j >= 0; --j) {
26                     if (v[j].cnt < tmp.cnt) {
27                         v[j+1] = v[j];
28                         mp[v[j+1].id] = j + 1;
29                     } else {
30                         break;
31                     }
32                 }
33                 v[j+1] = tmp;
34                 mp[tmp.id] = j+1;
35             }
36         }
37         
38         vector<string> topk(int n) {
39             vector<string> res;
40             for (int i = 0; i < n && i < v.size(); ++i) {
41                 res.push_back(v[i].id);
42             }
43             return res;
44         }
45 };
46 
47 int main() {
48     TopK tk;
49     vector<string> v;
50     tk.insert("bob");
51     tk.insert("joe");
52     tk.insert("bob");
53     tk.insert("jane");
54     tk.insert("joe");
55     tk.insert("bob");
56     tk.insert("jack");
57     v = tk.topk(2);
58     for (auto a : v) 
59         cout << a << " ";
60     cout << endl;
61     return 0;
62 }