[Google] 出现次数最多的前K个元素

bob, joe, bob, jane, bob, joe, jack

bob = 3 joe = 2

topN(2) = bob, joe .

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

 

用map<string, int>来存string在数组v中的下标，v存包含string与出现次数cnt的结构体，每次插入后动态调整v，使其按cnt从大到小有序。找前k个只要直接输出就是。

#include <bits/stdc++.h>
using namespace std;

class TopK {
    private:
        struct node {
            string id;
            int cnt;
            node(string _id, int _cnt) : id(_id), cnt(_cnt) {}
        };

        unordered_map<string, int> mp;
        vector<node> v;

    public:
        void insert(string s) {
            if (mp.find(s) == mp.end()) {
                v.push_back(node(s, 1));
                int idx = v.size() - 1;
                mp[s] = idx;
            } else {
                int idx = mp[s], j;
                ++v[idx].cnt;
                node tmp = v[idx];
                for (j = idx - 1; j >= 0; --j) {
                    if (v[j].cnt < tmp.cnt) {
                        v[j+1] = v[j];
                        mp[v[j+1].id] = j + 1;
                    } else {
                        break;
                    }
                }
                v[j+1] = tmp;
                mp[tmp.id] = j+1;
            }
        }
        
        vector<string> topk(int n) {
            vector<string> res;
            for (int i = 0; i < n && i < v.size(); ++i) {
                res.push_back(v[i].id);
            }
            return res;
        }
};

int main() {
    TopK tk;
    vector<string> v;
    tk.insert("bob");
    tk.insert("joe");
    tk.insert("bob");
    tk.insert("jane");
    tk.insert("joe");
    tk.insert("bob");
    tk.insert("jack");
    v = tk.topk(2);
    for (auto a : v) 
        cout << a << " ";
    cout << endl;
    return 0;
}