大家好，又见面了，我是你们的朋友全栈君。

1 输入输出重定向

FileInputStream inputStream = new FileInputStream("输入文件名");
System.setIn(inputStream);
//这个放在下面
Scanner input = new Scanner(System.in);

PrintStream outputStream = new PrintStream("输出文件");
System.setOut(outputStream);
Scanner input = new Scanner(System.in);

2 ACM中java快速输入输出 

P3367 【模板】并查集：https://blog.csdn.net/qq_40794973/article/details/103204372

https://blog.csdn.net/qq_40794973/article/details/88560643

java的Scanner 比较慢（出了名的了），如果需要输入数量级的数据并输出同样数量级的数据，使用Scanner和System.out耗时将很可能超过1s

2.1 使用 StreamTokenizer 和 PrintWriter

StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));

2.1.1 判断是否到达文件结尾

Java的while(scanner.hasNext())，或者C的while(scanf(“%d”,&n)!=EOF)

while (in.nextToken() != StreamTokenizer.TT_EOF) {
    //
}

伊格内修斯和公主四世：http://acm.hdu.edu.cn/showproblem.php?pid=1029

import java.io.*;
import java.util.HashMap;
public class Main {
    public static void main(String[] args) throws IOException {
        // io流包装
        StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        //StreamTokenizer.TT_EOF这个是个参数，就是EOF
        while (in.nextToken() != StreamTokenizer.TT_EOF) {
            int n = (int) in.nval;
            // 记录出现次数
            HashMap<Integer, Integer> appears = new HashMap<>();
            int max = 0;
            for (int i = 0; i < n; i++) {
                in.nextToken();//指向下一个
                int num = (int) in.nval;
                if (appears.containsKey(num)) {
                    Integer tempNum = appears.get(num);
                    appears.replace(num, tempNum + 1);
                    if (tempNum >= (n + 1) / 2) {
                        max = num;
                    }
                }else {
                    appears.put(num, 1);
                }
            }
            out.println(max);
            out.flush();//刷新，不然max会留在缓冲区
        }
    }
}