“腾讯服务器每秒有2w个QQ号同时上线，找出5min内重新登入的qq号并打印出来。”

#include <algorithm> #include <ctime> #include <iostream> #include <map> #include <vector> using namespace std; void timestamp() { time_t t = time(0); cout << ctime(&t) << endl; } // 模拟时钟 class PseudoTimer { int m_us; public: PseudoTimer() : m_us(0) {} int getMicroseconds() { return m_us += (rand() % 100); } // 登录平均间隔：1000000 / 20000 = 50微秒 }; /* hash表，表中保存最近一次登录时间 但这个表可能会增长（有用户长时间不登录），需要定时清除其中的旧记录 QQ号已经到10位了，8字节长整数保存 */ class HotUserMonitor { typedef long long QQ_t; struct UserStatus { int last_login_time; bool is_hot; UserStatus(int t, bool h) : last_login_time(t), is_hot(h) {} }; map<QQ_t, UserStatus> m_cache; static int const US_IN_5_MINUTES = 1000000 * 60 * 5; public: void login(QQ_t qq, int now) { map<QQ_t, UserStatus>::iterator p = m_cache.find(qq); if(p == m_cache.end()){ // qq号不在缓存中：保存时间、冷用户 m_cache.insert(make_pair(qq, UserStatus(now, false))); } else{ // 命中 p->second.last_login_time = now; // 更新最后登录时间 p->second.is_hot = ( (now - p->second.last_login_time) <= US_IN_5_MINUTES); // 超时：冷却 } } void scan_and_clean(int now) { int host_user_count = 0; for(map<QQ_t, UserStatus>::iterator p = m_cache.begin(); p != m_cache.end(); ){ if( (now - p->second.last_login_time) <= US_IN_5_MINUTES){ if(p->second.is_hot){ ++host_user_count; //cout << p->first << ' ' << p->second.first << ' ' << p->second.second << '/n'; // 热用户太多 } ++p; } else{ // overtime m_cache.erase(p++); } } cout << "hot user count: " << host_user_count << endl; } }; int main() { srand(time(0)); PseudoTimer pt; HotUserMonitor hsm; int const LOGIN_COUNT_IN_5_MINUTES = 20000 * 60 * 5; timestamp(); for( int i = 0; i < LOGIN_COUNT_IN_5_MINUTES; ++i){ // 模拟6000000次登录事件（20000 * 5 * 60） hsm.login(rand() * rand(), pt.getMicroseconds()); } timestamp(); hsm.scan_and_clean(pt.getMicroseconds()); timestamp(); return 0; }