数据库连接池

#include <iostream>
#include <fstream>
#include <algorithm>
#include <string>
#include <set>
using namespace std;

int main()
{
	int n;
	while (cin >> n)
	{
		set<string> pool;
		string id, con;
		int maxSize = 0;
		for (int i = 0; i < n; ++i)
		{
			cin >> id >> con;
			if (con == "connect") pool.insert(id);
			else if (con == "disconnect") pool.erase(id);
			int size = pool.size();
			maxSize = max(maxSize, size);
		}
		cout << maxSize << endl;
	}
	return 0;
}

import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            int n = sc.nextInt();
            int size = 0;
            int max = 0;
            for(int i = 0;i < n;i++){
                String id = sc.next();
                String s = sc.next();
                
                if(s.equals("connect")){
                    size++;
                    max = Math.max(max,size);
                }else if(s.equals("disconnect")){
                    size--;
                }
            }
            System.out.println(max);
        }
    }
}

#include <iostream>
#include <stdlib.h>
#include <string>
using namespace std;
int main() {
 int n;
 char id;
 string str;
 while (cin >> n) {
        int sum = 0;
     int max = 0;
  for (int i = 0; i < n; ++i) {
   cin >> id >> str;
   if (str == "connect") {
    sum++;
    if (sum > max) {
     max = sum;
    }
   }
   else if (str == "disconnect") {
    --sum;
   }
  }
  cout << max << endl;
 }
 system("pause");
 return 0;
}

python解法

使用一个列表来做，如果某个记录是connect，就加到列表中去，如果是disconnect，就把列表中对应的值删除掉。在加进去的过程中，不断判断列表的最大长度，最终返回这个最大长度即可。

while True:
    try:
        stack, maxNum = [], 0
        for _ in range(int(input())):
            left, right = input().split()
            if right == "connect":
                stack.append(left)
                maxNum = max(maxNum, len(stack))
            else:
                stack.remove(left)
        print(maxNum)
    except:
        break

#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<functional>
#include <map>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <exception>
#include <iomanip>
#include <memory>
#include <sstream>

using namespace std;

bool check(int x, int y, int m, int n, vector<vector<char>>& room)
{
	return x >= 0 && x < m && y >= 0 && y < n && room[x][y] == '.';
}

int main(int argc, char** argv)
{
	//freopen("in.txt", "r", stdin);
	int n;
	while (cin >> n)
	{
		unordered_set<string> connect;
		int count = 0;
		string id, op;
		while (n-- > 0)
		{
			cin >> id >> op;
			if (connect.find(id) != connect.end())
			{
				if (op == "disconnect")
					connect.erase(id);
			}
			else
			{
				if (op == "connect")
				{
					if (count == connect.size()) ++count;
					connect.emplace(id);
				}
			}
		}

		cout << count << endl;
	}

	return 0;
}

import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class _t354 {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		while(in.hasNext()){
			int n=in.nextInt(),rs=0;
			Queue<String> qe=new LinkedList<String>(); 
			for (int i = 0; i < n; i++) {
				String id=in.next();
				String status=in.next();
				qe.add(status);
			}
			
			int flag=0;
			for (int i = 0; i < n; i++) {
				if(qe.poll().equals("connect")){
					if(flag==0){
						rs++;
					}
					flag++;
				}
				else{
					flag--;
				}
			}
			System.out.println(rs);
		}
	}
}

try:
    while 1:
        maxVal, crnVal = 0, 0
        for i in xrange(input()):
            s = raw_input().split()
            if s[1] == "disconnect":
                crnVal -= 1
            else:
                crnVal += 1
                if crnVal > maxVal:
                    maxVal = crnVal
        print maxVal
except:
    pass

#include<stdio.h>


int main()
{
    char id[2], action[12];
    int n, pool, max;
    
    while(~scanf("%d", &n)){
        pool = max = 0;
        while(n--){
            scanf("%s%s", id, action);
            if(action[0] == 'c' && ++pool > max)
                 max = pool;
            if(action[0] == 'd')
                 --pool;
        }
        printf("%d\n", max);
    }
    return 0;
}

#include<iostream>
#include<string>
using namespace std;
int main()
{
    int n;
    while(cin>>n)
    {
        int count=0,max_count=0;
        string id,method;
        while(n--)
        {
            cin>>id>>method;//其实用不上id...
            if(method=="connect")     ++count;
            if(method=="disconnect")  --count;
            if(count>max_count)        max_count=count;
        }
        cout<<max_count<<endl;
    }
    return 0;
}

import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            int n = sc.nextInt();
            Set<String> s = new HashSet<>();
            int max_count = 0;
            while(n != 0){
                String id = sc.next();
                String op = sc.next();
                if(op.equals("connect")){
                    s.add(id);
                }else{
                    s.remove(id);
                }
                max_count = Math.max(max_count,s.size());
                n--;
            }
            System.out.println(max_count);
        }
    }
}

import java.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        while(scanner.hasNextLine()){
            String strNum = scanner.nextLine();
            int num = Integer.parseInt(strNum);
            int count = 0;
            int maxCount = 0;
            while(num-- != 0){
                String str = scanner.nextLine();
                if(!str.contains("disconnect")){
                    count++;
                }else{//那就是connect
                    maxCount = count > maxCount ? count : maxCount;
                    count--;
                }
            }
                System.out.println(maxCount);
            }
    }
}

import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            int n = Integer.parseInt(sc.nextLine());
            String[] str = new String[n];
            Stack<String> stack = new Stack<>();
            int max = 0;
            for(int i = 0; i < n; i++){
                str[i] = sc.nextLine();
                if(!str[i].contains("disconnect")){
                    stack.push(str[i]);
                    max = Math.max(max, stack.size());
                }
                else{
                    stack.pop();
                }
            }
            System.out.println(max);
        }
    }
}

//其实求解的就是最大连接数
#include<iostream>
#include<string>
using namespace std;
int main()
{
    int n;
    while(cin>>n)
    {
        int count=0,max_count=0;
        string id,status;
        while(n--)
        {
            cin>>id>>status;//这里id没用到，但是还必须按指定要求输入
            if(status == "connect") ++count;
            if(status == "disconnect") --count;
            if(count>max_count) max_count=count;
        }
        cout<<max_count<<endl;
    }
    return 0;
}

import java.util.*;

public class Main {
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        
        while (in.hasNextInt()) {
            int n = Integer.parseInt(in.next());
            int curLink = 0, maxLink = 0;
            Set<String> linkPool = new HashSet<>();
            for (int i = 0; i < n; ++i) {
                String name = in.next(), state = in.next();
                if (!linkPool.contains(name) && "connect".equals(state)) {
                    linkPool.add(name);
                    ++curLink;
                    maxLink = Math.max(curLink, maxLink);
                    continue;
                }
                
                if (linkPool.contains(name) && "disconnect".equals(state)) {
                    --curLink;
                    linkPool.remove(name);
                }
            }
            
            System.out.println(maxLink);
        }
        
        in.close();
    }
}

#include<iostream>
#include<string>
using namespace std;

int main()
{
    int n;
    while(cin>>n)
    {
        int max = 0;
        string con,oper;
        char c;
        while(n--)
        {
            cin>>c>>oper;
            if(oper[0]=='c')
                con.push_back(c);
            else
                con.erase(con.find(c),1);
            max = max<con.size() ? con.size() : max;
        }
        cout<<max<<endl;
    }
    return 0;
}