Fast I/O in Java

Scanner 类速度很慢

以下是 Java 中 Scanner 和 BufferedReader 类之间的主要区别

• BufferedReader 是同步的，而 Scanner 不是。如果我们使用多个线程，则应该使用 BufferedReader。
• BufferedReader 的缓冲内存比 Scanner 大得多。
• 与 BufferedReader（8KB 字节缓冲区）相比，Scanner 有一个小缓冲区（1KB 字符缓冲区），但绰绰有余。
• BufferedReader 比扫描器快一点，因为扫描器解析输入数据，而 BufferedReader 只是读取一个字符序列。

FastReader 模板

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class FastReaderMain {
    public static void main(String[] args) {
        FastReader s = new FastReader();
        int n = s.nextInt();
        int k = s.nextInt();
        int count = 0;
        while (n-- > 0) {
            int x = s.nextInt();
            if (x % k == 0) {
                count++;
            }
        }
        System.out.println(count);
    }

    private static class FastReader {
        private final BufferedReader bufferedReader;
        private StringTokenizer stringTokenizer;

        public FastReader() {
            bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        }

        public String next() {
            while (stringTokenizer == null || !stringTokenizer.hasMoreElements()) {
                try {
                    stringTokenizer = new StringTokenizer(bufferedReader.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return stringTokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }

        public String nextLine() {
            String str = "";
            try {
                if (stringTokenizer.hasMoreTokens()) {
                    str = stringTokenizer.nextToken("\n");
                } else {
                    str = bufferedReader.readLine();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
}

Reader 模板

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;

public class ReaderMain {
    public static void main(String[] args) throws IOException {
        Reader s = new Reader();
        int n = s.nextInt();
        int k = s.nextInt();
        int count = 0;
        while (n-- > 0) {
            int x = s.nextInt();
            if (x % k == 0) {
                count++;
            }
        }
        System.out.println(count);
    }

    static class Reader {
        private final int BUFFER_SIZE = 1 << 16;
        private final DataInputStream dataInputStream;
        private final byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader() {
            dataInputStream = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException {
            dataInputStream = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1) {
                if (c == '\n') {
                    if (cnt != 0) {
                        break;
                    } else {
                        continue;
                    }
                }
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException {
            int ret = 0;
            byte c = read();
            while (c <= ' ') {
                c = read();
            }
            boolean neg = (c == '-');
            if (neg) {
                c = read();
            }
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (neg) {
                return -ret;
            }
            return ret;
        }

        public long nextLong() throws IOException {
            long ret = 0;
            byte c = read();
            while (c <= ' ') {
                c = read();
            }
            boolean neg = (c == '-');
            if (neg) {
                c = read();
            }
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (neg) {
                return -ret;
            }
            return ret;
        }

        public double nextDouble() throws IOException {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ') {
                c = read();
            }
            boolean neg = (c == '-');
            if (neg) {
                c = read();
            }
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (c == '.') {
                while ((c = read()) >= '0' && c <= '9') {
                    ret += (c - '0') / (div *= 10);
                }
            }
            if (neg) {
                return -ret;
            }
            return ret;
        }

        private void fillBuffer() throws IOException {
            bytesRead = dataInputStream.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1) {
                buffer[0] = -1;
            }
        }

        private byte read() throws IOException {
            if (bufferPointer == bytesRead) {
                fillBuffer();
            }
            return buffer[bufferPointer++];
        }

        public void close() throws IOException {
            dataInputStream.close();
        }
    }
}

参考链接

• Fast I/O in Java in Competitive Programming