wrick's blog

By wrick, history, 7 years ago, In English

We all know that java.util.Scanner is slow.

Here is a version in Scala that is idiomatic (you can do all the Collections API e.g. .take, .map, .filter etc) and supports line numbers too and is much faster than the Java Scanner:

import java.io._
import java.nio.file.{Files, Path}
import java.util.StringTokenizer

import scala.io.Codec

 * Scala implementation of a faster java.util.Scanner
 * See: http://codeforces.com/blog/entry/7018
class Scanner(reader: LineNumberReader) extends Iterator[String] with AutoCloseable {
  def this(reader: BufferedReader) = this(new LineNumberReader(reader))
  def this(reader: Reader) = this(new BufferedReader(reader))
  def this(inputStream: InputStream)(implicit codec: Codec) = this(new InputStreamReader(inputStream, codec.charSet))
  def this(path: Path)(implicit codec: Codec) = this(Files.newBufferedReader(path, codec.charSet))
  def this(file: File)(implicit codec: Codec) = this(file.toPath)(codec)
  def this(str: String) = this(new StringReader(str))

  private[this] val tokenizers = Iterator.continually(reader.readLine()).takeWhile(_ != null).map(new StringTokenizer(_)).filter(_.hasMoreTokens)
  private[this] var current: Option[StringTokenizer] = None

  @inline private[this] def tokenizer(): Option[StringTokenizer] = current.find(_.hasMoreTokens) orElse {
    current = if (tokenizers.hasNext) Some(tokenizers.next()) else None

   * Unlike Java's scanner which returns till end of current line, this actually returns the next line
   * @see line() if you want the Java behaviour
  def nextLine(): String = {
    current = None   // reset
  def lineNumber: Int = reader.getLineNumber
  def line(): String = tokenizer().get.nextToken("\n\r")
  def nextString(): String = next()
  def nextChar(): Char = next().ensuring(_.length == 1).head
  def nextBoolean(): Boolean = next().toBoolean
  def nextByte(radix: Int = 10): Byte = java.lang.Byte.parseByte(next(), radix)
  def nextShort(radix: Int = 10): Short = java.lang.Short.parseShort(next(), radix)
  def nextInt(radix: Int = 10): Int = java.lang.Integer.parseInt(next(), radix)
  def nextLong(radix: Int = 10): Long = java.lang.Long.parseLong(next(), radix)
  def nextBigInt(radix: Int = 10): BigInt = BigInt(next(), radix)
  def nextFloat(): Float = next().toFloat
  def nextDouble(): Double = next().toDouble
  def nextBigDecimal(): BigDecimal = BigDecimal(next())
  override def next() = tokenizer().get.nextToken()
  override def hasNext = tokenizer().nonEmpty
  override def close() = reader.close()

Source: https://github.com/pathikrit/ScalaForces/blob/master/src/main/scala/Scanner.scala

Benchmarks: https://github.com/pathikrit/better-files/tree/master/benchmarks

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7 years ago, # |
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Auto comment: topic has been updated by wrick (previous revision, new revision, compare).