25.4.3学习总结【Java】

又是一道错题：

1. 班级活动https://www.lanqiao.cn/problems/17153/learning/?page=1&first_category_id=1&sort=difficulty&asc=1&second_category_id=3

问题描述

小明的老师准备组织一次班级活动。班上一共有 n 名 (n 为偶数) 同学，老师想把所有的同学进行分组，每两名同学一组。为了公平，老师给每名同学随机分配了一个 n 以内的正整数作为 id，第 i 名同学的 id 为 ai。

老师希望通过更改若干名同学的 id 使得对于任意一名同学 i，有且仅有另一名同学 j 的 id 与其相同 (ai=aj)。请问老师最少需要更改多少名同学的 id？

输入格式

输入共 2 行。

第一行为一个正整数 n。

第二行为 n 个由空格隔开的整数 a1,a2,...,an​。

输出格式

输出共 1 行，一个整数。

评测用例规模与约定

对于 20%的数据，保证 n≤10^3。

对于 100%的数据，保证 n≤10^5。

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{int a;scanf("%d",&a);int *b=(int*)calloc(100005,sizeof(int));for(int i=0;i<a;i++){int temp;scanf("%d",&temp);b[temp]++;}int count=0;for(int i=0;i<100005;i++){if(b[i]>2)count+=(b[i]-2);if (b[i]==1)count++;}printf("%d\n",count/2);free(b);return 0;
}

对上次的题再次的错解28/54：

#define max(a,b) (((a)>(b))?(a):(b))
long long mostPoints(int questions[][2], int questionsSize, int* questionsColSize) {long long record[questionsSize+1];for(int i=0;i<questionsSize+1;i++) {record[i] = 0;}for(int i=0;i<questionsSize;i++) {const int temp=i+1+questions[i][1],prior=record[i];record[i]=record[i]+questions[i][0];if (temp<questionsSize) {record[temp]=max(record[temp],record[i]);}else {record[questionsSize]=max(prior+questions[i][0],record[questionsSize]);}}return max(record[questionsSize-1],record[questionsSize]);
}

 网络编程(作业)：

import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.Socket;
import java.util.Scanner;public class d1 {public static void main(String[] args) throws IOException {Socket socket = new Socket("127.0.0.1", 10000);System.out.println("用户3");new Thread(()->{try(InputStreamReader isr = new InputStreamReader(socket.getInputStream())){char []data = new char[1024];int len;while((len=isr.read(data))!=-1){System.out.print("【群消息】"+new String(data,0,len));}}catch(IOException e){System.out.println("连接已断开！");}}).start();try(OutputStream os = socket.getOutputStream()){Scanner sc = new Scanner(System.in);while(true){String s = sc.nextLine();if(s.equals("exit"))break;os.write((s+"\n").getBytes());}}socket.close();}
}

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.atomic.AtomicInteger;
public class d2 {static CopyOnWriteArrayList<Socket> list=new CopyOnWriteArrayList<>();static AtomicInteger count=new AtomicInteger(0);public static void main(String[] args) throws IOException {ServerSocket serverSocket = new ServerSocket(10000);System.out.println("服务器成功启动！");while (true) {Socket socket = serverSocket.accept();list.add(socket);new Thread(new d3(socket,count.incrementAndGet())).start();}}
}

import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;
public class d3 implements Runnable {Socket socket;int num;public d3(Socket socket,int num) {this.socket = socket;this.num = num;}@Overridepublic void run() {InputStreamReader in;try {in = new InputStreamReader(socket.getInputStream());} catch (IOException e) {throw new RuntimeException(e);}int temp;StringBuilder message = new StringBuilder();System.out.println("用户"+num+"连接成功！当前在线人数为:"+d2.list.size());while (true) {try {if ((temp = in.read()) == -1) break;} catch (IOException e) {throw new RuntimeException(e);}if((char)temp!='\n')message.append((char)temp);else {broadcast(message.toString());message.setLength(0);}}d2.list.remove(socket);String temp1="用户"+num+"断开连接！剩余在线："+d2.list.size();System.out.println(temp1);broadcast(temp1);try {socket.close();} catch (IOException e) {throw new RuntimeException(e);}}public void broadcast(String message){for(Socket list :d2.list){try{if (list != socket && !list.isClosed()) {list.getOutputStream().write(("用户"+num+":"+message + "\n").getBytes());}}catch (Exception e){d2.list.remove(list);}}}
}