enhanced map with random

exmap.cpp

#include <vector>
#include <map>
#include <utility>
#include <iostream>

using namespace std;

class ExMap {
    map<int, int> _map; // key to index of _keyVals
    vector<pair<int,int>> _keyVals;

public:
    ExMap() {
        srand(time(NULL));
    }

   void set(int key, int value);
   bool hasKey(int key);
   int get(int key);
   void remove(int key);
   int random();
};

void ExMap::set(int key, int value) {
    if (!hasKey(key)) {
        _keyVals.push_back(make_pair(key, value));
        _map[key] = _keyVals.size() - 1;    
    } else {
        _keyVals[_map[key]].second = value;  
    }
}

bool ExMap::hasKey(int key) {
    return _map.find(key) != _map.end();
}

int ExMap::get(int key) {
    return _keyVals[_map[key]].second;
}

void ExMap::remove(int key) {
    if (hasKey(key)) {
        int idx = _map[key];
        int tail = _keyVals.size() - 1;
        _keyVals[idx] = _keyVals[tail];
        _map.erase(key);
        _keyVals.pop_back();
    }
}

int ExMap::random() {
    int idx = rand() % _keyVals.size();
    return _keyVals[idx].second;
}

int main() {
    ExMap em;
    cout << "============basic test ============" << endl;
    em.set(1,2);
    em.set(2,3);
    cout << em.get(1) << endl;
    cout << em.get(2) << endl;
    em.set(2,4);
    cout << em.get(2) << endl;
    em.remove(2);
    cout << em.hasKey(2) << endl;
    cout << "============random test ============" << endl;
    for (int i = 0; i < 10; i++) {
        em.set(i, i*10 + i);
    }
    map<int, int> count;
    for (int i = 0; i < 100000; i++) {
        int r = em.random();
        if (count.find(r) == count.end()) {
            count[r] = 1;   
        } else {
            count[r]++;
        }
    }
    for (auto iter = count.begin(); iter != count.end(); iter++) {
        cout << iter->first << ":" << iter->second << endl;
    }
    cout << "============random after remove test ============" << endl;
    count.clear();
    
    for (int i = 0; i < 100000; i++) {
        int r = em.random();
        if (count.find(r) == count.end()) {
            count[r] = 1;   
        } else {
            count[r]++;
        }
    }

    em.remove(7);
    em.remove(2);
    for (int i = 0; i < 100000; i++) {
        int r = em.random();
        if (count.find(r) == count.end()) {
            count[r] = 1;   
        } else {
            count[r]++;
        }
    }
    for (auto iter = count.begin(); iter != count.end(); iter++) {
        cout << iter->first << ":" << iter->second << endl;
    }
    return 0;
}

/*
============basic test ============
2
3
4
0
============random test ============
0:9999
11:9871
22:9855
33:10173
44:10014
55:10055
66:10043
77:10029
88:9973
99:9988
============random after remove test ============
0:22527
11:22579
22:9982
33:22731
44:22485
55:22408
66:22653
77:9964
88:22287
99:22384
*/