构造 Codeforces Round #Pi (Div. 2) B. Berland National Library

题目传送门

 /*
     题意：给出一系列读者出行的记录，+表示一个读者进入，-表示一个读者离开，可能之前已经有读者在图书馆
     构造：now记录当前图书馆人数，sz记录最小的容量，in数组标记进去的读者，分情况讨论一下
 */
 /************************************************
 * Author        :Running_Time
 * Created Time  :2015-8-6 0:23:37
 * File Name     :B.cpp
  ************************************************/

 #include <cstdio>
 #include <algorithm>
 #include <iostream>
 #include <sstream>
 #include <cstring>
 #include <cmath>
 #include <string>
 #include <vector>
 #include <queue>
 #include <deque>
 #include <stack>
 #include <list>
 #include <map>
 #include <set>
 #include <bitset>
 #include <cstdlib>
 #include <ctime>
 using namespace std;

 #define lson l, mid, rt << 1
 #define rson mid + 1, r, rt << 1 | 1
 typedef long long ll;
 const int MAXN = 1e6 + ;
 const int INF = 0x3f3f3f3f;
 const int MOD = 1e9 + ;
 bool in[MAXN];

 int main(void)    {     //Codeforces Round #Pi (Div. 2) B. Berland National Library
     int n;  scanf ("%d", &n);
     memset (in, false, sizeof (in));
     int now = , sz = ;
     for (int i=; i<=n; ++i)    {
         char s[];    int x;  scanf ("%s%d", &s, &x);
         if (s[] == '+')  {
             now++;  in[x] = true;
             if (now > sz)   sz++;
         }
         else if (s[] == '-')   {
             if (now == )   {
                 if (in[x])  in[x] = false;
                 sz++;
             }
             else    {
                 if (!in[x]) {       //是之前就进入图书馆的读者
                     sz++;
                 }
                 else    {
                     in[x] = false;  now--;
                 }
             }
         }
     }

     printf ("%d\n", sz);

     return ;
 }