Java in ACM/ICPC

Directory

• The features of Java in ACM/ICPC

• Issues to be aware of when using Java in ACM/ICPC

• Java and high-precision computing

Features of the 1.Java in ACM/ICPC

Java syntax is almost the same as C + +

Java is not much slower than C + + in performing compute-intensive tasks, just slower IO operations

Java is simple and powerful, and some things are more convenient to implement in Java.

For example: input and output, string parsing, high precision

Java is not easy to make subtle mistakes

A pointer in C + +

"if (n = m) ... ”

Java and Eclipse

2. Issues to be aware of when using Java in ACM/ICPCJava Program Structure

Java I/O

JDK1.5.0 new Scanner class is well suited for AMC/ICPC input

General steps for using the Scanner class

1. Import the Scanner class

Import Java.util.Scanner;

2. Creating an object of the scanner class

Scanner cin=new Scanner (system.in); Read data from standard input

Scanner cin=new Scanner ("12 30")); Reading data from a string

3. Read all types of data using objects of the scanner class

Cin.nextint ()

Cin.nextdouble ();

...

Common methods of the scanner Class 1. Read data

Scanner class method	corresponding to C operation	Corresponds to C + + operations
int n = cin.nextint ();	scanf ("%d", &n);	CIN >> N;
String s = cin.next ();	scanf ("%s", s);	Cin >> S;
Double T = cin.nextdouble ();	scanf ("%lf", &t);	CIN >> T;
String s = cin.nextline ();	Gets (s);	Cin.getline (...);
BigDecimal B=cin.nextbigdecimal ();

2. Determine if there is any data

Cin.hasnext () or cin.hasnextint () or cin.hasnextdouble ()

Examples of methods for scanner classes:

import java.util.*;  Public class main{    publicstaticvoid  Main (string[] args) {        Scanner sc= New Scanner (system.in);          while (Sc.hasnext ()) {            char ch= (char) sc.nextint ();            System.out.print (CH);      }}}

Standard output System.out.print (...);  Do not output line break System.out.println (...); Output line break

import java.io.*;  Public class main{    static printstream cout=system.out;      Public Static void Main (string[] args) {        int n=3,m=5;        COUT.PRINTLN (n);   // Output 3          // output multiple integers on the same line can be used        Cout.println (n+ "" +m);    }}

Controlling floating-point number decimal digits with the DecimalFormat class

Import Java.text.DecimalFormat;

Control method

Constructs a specific DecimalFormat object: DecimalFormat f=new decimalformat ("#.00#");

The arguments in the constructor are pattern strings, 0 refers to one digit, #指除0以外的数字

Use the Decimaformat object to format the floating-point number that needs to be output: System.out.println (F.format (12.1234));

DecimalFormat Example

import java.text.*;  Public class decimalformat{    publicstaticvoid  main (string[] args) {          New DecimalFormat ("#.00#");         New DecimalFormat ("0.000");         double a = 123.4509, B = 0.12;        System.out.println (F.format (a));        System.out.println (G.format (a));        System.out.println (F.format (b));        System.out.println (G.format (b));}    }

Operation Result:

123.451

123.451

.12

0.120

Another way to format the output is to use the System.out.printf ("format string",...), whose usage is basically consistent with the C printf

int a=10; float b=2.35f; System.out.printf (

Strings (String)

Common methods of the string class:

Construct the string:

String s="ABCDE"; Char [] chs={' A ', ' B ', ' C ', ' d ', ' e '}; string s=new string (CHS);

Get a character in a string:

Char Ch=s.charat (1);    // ch= ' B ';

Seek substring:

// output "abc" // output "BC" // output "BCDE"

Split string:

String s= "123:34:55= s.split (": ");  for (int i=0;i<ss.length;i++) System.out.println (Ss[i]);

Operation Result:

123

34

55

Replacement string:

String s= "2009-07-26"; System.out.println (S.replace ('-'), '/ /// output 2009/07/26String s= "0.123456 "; System.out.println (S.replaceall ("// output. 123456

The characters in string cannot be changed and can be used if changes are required StringBuffer

Other matters to note

A Java array is an object that must be initialized after definition, such as int[] a = new int[100]; Array lengths are obtained by length members, such as SYSTEM.OUT.PRINTLN (A.length);

The Arrays class provides some useful methods:

Arrays.fill ()

Arrays.sort ()

Arrays.binarysearch ()

The Boolean type is Boolean, with only true and false two values, which must be a Boolean type in the conditions of the IF (...)/while (...) statement.

if (n% 2) in C + + ... cannot be compiled in Java.

Java also provides an STL-like collection class:

Vector,arraylist,map,queue,stack,hashtable

3.Java and high-precision computing Pku1001-exponentiation (exponentiation):

Sample Input

95.123 12

0.4321 20

5.1234 15

6.7592 9

98.999 10

1.0100 12

Sample Output

548815620517731830194541.899025343415715973535967221869852721

. 00000005148554641076956121994511276767154838481760200726351203835

429763013462401

43992025569.928573701266488041146654993318703707511666295476720493

953024

29448126.764121021618164430206909037173276672

90429072743629540498.107596019456651774561044010001

1.126825030131969720661201

Methods for solving in C + +

The POW function is not able to achieve the required precision

Use arrays to simulate multiplication for improved accuracy

Java code:

Importjava.math.*;ImportJava.util.*; Public classmain{ Public Static voidMain (string[] args) {Scanner in=NewScanner (system.in);  while(In.hasnext ()) {BigDecimal Val=In.nextbigdecimal (); intn=In.nextint (); BIGDECIMAL ret=Val.pow (n). Striptrailingzeros (); System.out.println (Ret.toplainstring (). ReplaceAll ("^0", "" ") ); }    }}

BigDecimal class

High-precision signed decimal number constructs a high-precision number

BigDecimal (int val)

BigDecimal (double val)

BigDecimal (String val)

BigDecimal d1=New BigDecimal (1); BigDecimal d2=new BigDecimal (0.1); BigDecimal d3=new BigDecimal ("0.1");        System.out.println ("d1=" +D1); System.out.println ("d2=" +D2); System.out.println ("d3=" +d3);

Common methods of the BigDecimal class:

BigDecimal Add (BigDecimal augend)//"+"BigDecimal Subtract (BigDecimal subtrahend)//"-"BigDecimal Multiply (BigDecimal multiplicand)//"*"BigDecimal Divide (BigDecimal divisor)//"/"BigDecimal remainder (BigDecimal divisor)//"%"BigDecimal Pow (intN//"exponentiation"String toplainstring ()//returns a string representation without an exponentString toString ()//returns a string representation with an exponent

PKU High-precision calculation topics:

1131, 1205, 1220, 1405, 1503, 1604 1894, 2084, 2305, 2325, 2389, 2413 3101, 3199

Java in ACM/ICPC