题意：模拟买卖，当出售价bid等于或低于出售价ask，则交易。
代码：（Accepted，0.330s）
//UVa1598 - Exchange //Accepted 0.330s //#define _XIENAOBAN_ #include<functional> #include<algorithm> #include<iostream> #include<utility> #include<vector> #include<queue> #include<map> #include<set> using namespace std; struct INFO { char type; int size, price; }for_push_back; int N, T(0); char type[20]; vector<INFO> LIST; //key: buy/ask id, value: type, size map<int, set<int>, greater<int> > BUY; //key: bid price, value: id map<int, set<int>, less<int> > SELL; //key: ask price, value: id map<int, int> BUY_VAL; //key: bid price, value: size map<int, int> SELL_VAL; //key: ask price, value: size inline int sum(set<int>& now) { int re(0); for (const auto& r : now) re += LIST[r].size; return re; } void trade(bool flag) { int bid_size, bid_price, ask_size, ask_price; while (true) { auto bid(BUY.begin()), ask(SELL.begin()); if (bid == BUY.end()) bid_size = 0, bid_price = 0; else bid_size = BUY_VAL[bid->first], bid_price = bid->first; if (ask == SELL.end()) ask_size = 0, ask_price = 999999; else ask_size = SELL_VAL[ask->first], ask_price = ask->first; if (bid_price < ask_price) { printf("QUOTE %d %d - %d %d\n", bid_size, bid_price, ask_size, (ask_price == 999999 ? 99999 : ask_price)); return; } auto sizeb(LIST[*bid->second.begin()].size), sizea(LIST[*ask->second.begin()].size); const auto mini(min(sizeb, sizea)); printf("TRADE %d %d\n", mini, flag ? ask_price : bid_price); auto& b(bid->second), &a(ask->second); BUY_VAL[bid->first] -= mini; if (!b.empty() && (LIST[*b.begin()].size -= mini) == 0) b.erase(b.begin()); if (b.empty()) BUY.erase(bid); SELL_VAL[ask->first] -= mini; if (!a.empty() && (LIST[*a.begin()].size -= mini) == 0) a.erase(a.begin()); if (a.empty()) SELL.erase(ask); } } int main() { #ifdef _XIENAOBAN_ #define gets(T) gets_s(T, 66666) freopen("in.txt", "r", stdin); freopen("out.txt", "w", stdout); #endif while (scanf("%d", &N) != EOF) { if (T++) puts(""); LIST.clear(), BUY.clear(), SELL.clear(), BUY_VAL.clear(), SELL_VAL.clear(); LIST.push_back(for_push_back); for (int n(1);n <= N;++n) { INFO tmp; scanf("%s", type); if (*type == 'C') { int id; scanf("%d", &id); auto& csl(LIST[id]); if (csl.type == 'B') { BUY_VAL[csl.price] -= csl.size; LIST[id].size = 0; auto& now(BUY[csl.price]); now.erase(id); if (now.empty()) BUY.erase(csl.price); } else { SELL_VAL[csl.price] -= csl.size; LIST[id].size = 0; auto& now(SELL[csl.price]); now.erase(id); if (now.empty()) SELL.erase(csl.price); } } else { tmp.type = *type; scanf("%d%d", &tmp.size, &tmp.price); if (*type == 'B') BUY[tmp.price].insert(n), BUY_VAL[tmp.price] += tmp.size; else SELL[tmp.price].insert(n), SELL_VAL[tmp.price] += tmp.size; } LIST.push_back(std::move(tmp)); trade(*type == 'B'); } } return 0; }分析：书上推荐使用优先队列，然而并没有想出来怎么去用。想了想还是用了map，用它的begin()，效果一样的，还可以灵活差入数据。一开始老是在某组测试数据上出现Runtime error，搞得生无可恋。（从一老司机学到的新技能：当提交OJ出现RE时（WA也行），在执行每组数据计算的代码末尾加一句“while(1);”再提交如果从RE变成TLE了则说明是某些特殊数据没照顾到。毕竟不是所有OJ都有udebug可以用，这招还是不错的） 然后过了一天还是心里放不下，又回来想了想，是题目中一个细节“If there is no active order to sell, then it is assumed that ask size is zero and ask price is 99 999. Note, that zero is not a legal price, but 99 999 is a legal price. Recipient of quote messages distinguishes actual 99 999 ask price from the special case of absent orders to sell by looking at its ask size.”出了问题。于是把不可交易价格改成999999，与交易最大价格加以99999区分，果然似乎没问题了。然而接下来就有新问题，Time limit exceeded。。。 又过了一天，心里还是放不下，于是去网上查了查别人的代码，他们不仅用两个map存买卖信息，还再单独开辟两个map来存放sell与buy的总size（就相当于我上面那两个BUY_VAL 和 SELL_VAL），而当时我只用了两个map（BUY和SELL）存买卖的所有信息，所以每次查询循环总的size时要经历一个比较烦的循环，就是以下这个循环：
//求当前价格总的size函数 int sum(set<int>& now) { int re(0); for (const auto& r : now) re += LIST[r].size; return re; } //trade函数片段 auto bid(BUY.begin()), ask(SELL.begin()); if (bid == BUY.end()) bid_size = 0, bid_price = 0; else bid_size = sum(bid->second), bid_price = bid->first; if (ask == SELL.end()) ask_size = 0, ask_price = 999999; else ask_size = sum(ask->second), ask_price = ask->first;这就是超时的罪魁祸首。改进了下瞬间变成0.330s，还是有些出乎意料。
转载于:https://www.cnblogs.com/xienaoban/p/6798080.html
