Java's Scanner : our implementation

On France-IOI, we are using the gcj compiler to compile Java's source codes into executables.

We have our own implementation of the Java's Scanner.

• It fixes speed and memory usage problems (see below).
• It fixes some gcj's Scanner "bugs" (see below)
• It hasn't all the original functions

Example of use

Exactly as you would use the original Java's Scanner :

Scanner sc = new Scanner(System.in);
int val = sc.nextInt()

Supported functions

Original functions :

public boolean hasNext();
public String next();
public String nextLine();
public int nextInt();
public long nextLong();
public float nextFloat();
public double nextDouble();

Added functions :

public char nextChar();

Bugs fixed

Using nextDouble() to read the value 0 raises the error ava.util.InputMismatchException: "0" is not a double.

See http://stackoverflow.com/questions/9055788/java-scanner-0-is-not-a-double for more details.

Our Scanner fixes that

Speed and memory usage

For this benchmark we are reading N integers on standard input, the most common usage in algorithmic contests.

  Comparison of Java's Scanner / our Scanner

  For 10 integers :
  Time : .07s vs .07s
  Memory : 25164K vs 20760K
  Ratios (time/mem) : 1.0 and 1.2

  For 5000 integers :
  Time : .26s vs .08s
  Memory : 30036K vs 21596K
  Ratios (time/mem) : 3.2 and 1.3

  For 10000 integers :
  Time : .44s vs .06s
  Memory : 30956K vs 22380K
  Ratios (time/mem) : 7.3 and 1.3

  For 25000 integers :
  Time : 1.02s vs .07s
  Memory : 34464K vs 23704K
  Ratios (time/mem) : 14.5 and 1.4

  For 50000 integers :
  Time : 1.97s vs .11s
  Memory : 39596K vs 25788K
  Ratios (time/mem) : 17.9 and 1.5

  For 75000 integers :
  Time : 2.93s vs .20s
  Memory : 44988K vs 26060K
  Ratios (time/mem) : 14.6 and 1.7

  For 100000 integers :
  Time : 3.85s vs .23s
  Memory : 50456K vs 26056K
  Ratios (time/mem) : 16.7 and 1.9

  For 150000 integers :
  Time : 5.68s vs .27s
  Memory : 60648K vs 26060K
  Ratios (time/mem) : 21.0 and 2.3

  For 200000 integers :
  Time : 6.86s vs .37s
  Memory : 75148K vs 26320K
  Ratios (time/mem) : 18.5 and 2.8