zoj - 3309- Search New Posts

来源：互联网发布：淘宝家具店编辑：程序博客网时间：2024/06/04 22:43

题意：给一个操作和一个话题，操作有， new（加入新话题）， reply（某话题置顶，同时当作新话题）， tag（把某话题标记为旧话题）， serach（从top到bottom输出前100个新话题）。

解法：话题存在一个双向链表中（方便删除和插入），每个话题名称映射一个链表的节点（用map），然后就是模拟。

坑点：一个话题可以被tag多次，导致一开始访问了空指针（如果用链表做注意）。

//code

#include<iostream>#include<cstdio>#include<string>#include<list>#include<map>using namespace std;struct List{List *prev;List *next;string name;friend bool operator < (List a, List b){return a.name<b.name;}};int main(){int n;while(cin>>n){map<string, List*>_m;map<string, List*>::iterator it;List *_l, *Head;Head = new List;_l = new List;_l->name = "Last";_l->next = NULL;_l->prev = Head;Head->next=_l;Head->name = "Head";Head->prev = NULL;for(int i=0; i<n; i++){string tmp;cin>>tmp;if(tmp == "new"){cin>>tmp;List *_l_tmp;_l_tmp = new List;_l_tmp->name = tmp;_l_tmp->next = Head->next;_l_tmp->prev = Head;Head->next = _l_tmp;_l_tmp->next->prev = _l_tmp;_m.insert(map<string, List*>::value_type(_l_tmp->name, _l_tmp));}else if(tmp == "reply"){cin>>tmp;it = _m.find(tmp);if(it == _m.end()) continue;List *Prev, *Next;Prev = it->second->prev;Next = it->second->next;if(Prev != NULL && Next != NULL){Prev->next = Next;Next->prev = Prev;}it->second->next = Head->next;it->second->prev = Head;Head->next = it->second;it->second->next->prev = it->second;}else if(tmp == "tag"){cin>>tmp;it = _m.find(tmp);if(it == _m.end()) continue;if(it->second->next == NULL && it->second->prev == NULL) continue;List *Prev, *Next;Prev = it->second->prev; Next = it->second->next;Prev->next = Next;Next->prev = Prev;it->second->next = it->second->prev = NULL;}else if(tmp == "search"){List *q;q = Head->next;int Sum=0;while(q->next != NULL){cout<<q->name<<endl;Sum++;if(Sum >= 100) break;q = q->next;}cout<<"###"<<endl;}}printf("\n");}return 0;}