Java在ACM中的应用

输入：可以从文件中输入，也可以从控制台输入。

import java.io.BufferedInputStream;
import java.io.File;
import java.util.Scanner;

public class Demo {

public static void main(String[] args) throws Exception {
Scanner cin = null;
cin = new Scanner(new File("data.in"));// 从文件读取
// cin = new Scanner(new BufferedInputStream(System.in));// 从控制台输入
int a = -1;
while (cin.hasNext()) {
a = cin.nextInt();
System.out.println(a);
}
cin.close();
}

}

cin.nextType(); // 的某种类型的数，其中Type=Double,Float,Byte,Short,Int,Long,Boolean,BigInteger,BigDecimal
cin.next();// 遇到空格返回，即得到一个字符串
cin.nextLine();// 遇到换行符返回，即得到一行字符串

应用最多的应是Java中的大数类：

BigInteger

// 以下是BigInteger数的加、减、乘、除与取余
public static BigInteger add(BigInteger a, BigInteger b) {
return a.add(b);
}

public static BigInteger subtract(BigInteger a, BigInteger b) {
return a.subtract(b);
}

public static BigInteger multiply(BigInteger a, BigInteger b) {
return a.multiply(b);
}

public static BigInteger divide(BigInteger a, BigInteger b) {
return a.divide(b);
}

public static BigInteger mod(BigInteger a, BigInteger b) {
return a.mod(b);
}

BigDecimal

// 以下是BigDecimal数的加、减、乘、除
public static BigDecimal add(BigDecimal a, BigDecimal b) {
return a.add(b);
}

public static BigDecimal subtract(BigDecimal a, BigDecimal b) {
return a.subtract(b);
}

public static BigDecimal multiply(BigDecimal a, BigDecimal b) {
return a.multiply(b);
}

public static BigDecimal divide(BigDecimal a, BigDecimal b) {
return a.divide(b);
}

Arrays类中的应用：排序（sort）,填充（fill）,二分查询（binarySearch）

排序：

int[] arr = new int[] { 12, -2, 3, -1, 22, 7 };
for (int i : arr) {
System.out.println(i);
}
Arrays.sort(arr);// 从小到大
System.out.println("---排序---");
for (int i : arr) {
System.out.println(i);
}

// result:
// 12
// -2
// 3
// -1
// 22
// 7
// ---排序---
// -2
// -1
// 3
// 7
// 12
// 22

引用类型排序：

import java.io.BufferedInputStream;
import java.util.Iterator;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeSet;

public class Demo {

public static void main(String[] args) throws Exception {
Scanner cin = new Scanner(new BufferedInputStream(System.in));
Set<Student> set = null;
Iterator<Student> ite = null;
Student stu = null;
String str = null;
String[] strStu = null;
int num = -1;
while (cin.hasNext()) {
str = cin.nextLine();
num = Integer.parseInt(str);
set = new TreeSet<Student>();
for (int i = 0; i < num; i++) {
str = cin.nextLine();
strStu = str.split(" ");
stu = new Student(Integer.parseInt(strStu[0]), strStu[1],
Double.parseDouble(strStu[2]));
set.add(stu);
}
ite = set.iterator();
while (ite.hasNext()) {
stu = ite.next();
System.out.println(stu);
}
}
cin.close();
}

// result:
// 10
// 22 limin 90
// 12 limin 99
// 33 limin 78
// 9 zhaolin 100
// 0 zhaolin 90
// 2 zhaolin 99
// 88 wanzai 100
// 7 zhaolin 100
// 3 linmin 90
// 10 wanzai 99
// Student [sid=33, sname=limin, sscore=78.0]
// Student [sid=22, sname=limin, sscore=90.0]
// Student [sid=3, sname=linmin, sscore=90.0]
// Student [sid=0, sname=zhaolin, sscore=90.0]
// Student [sid=12, sname=limin, sscore=99.0]
// Student [sid=10, sname=wanzai, sscore=99.0]
// Student [sid=2, sname=zhaolin, sscore=99.0]
// Student [sid=88, sname=wanzai, sscore=100.0]
// Student [sid=7, sname=zhaolin, sscore=100.0]
// Student [sid=9, sname=zhaolin, sscore=100.0]

}

class Student implements Comparable<Student> {
private int sid;
private String sname;
private double sscore;

public int getSid() {
return sid;
}

public void setSid(int sid) {
this.sid = sid;
}

public String getSname() {
return sname;
}

public void setSname(String sname) {
this.sname = sname;
}

public double getSscore() {
return sscore;
}

public void setSscore(double sscore) {
this.sscore = sscore;
}

@Override
public String toString() {
return "Student [sid=" + sid + ", sname=" + sname + ", sscore="
+ sscore + "]";
}

public Student(int sid, String sname, double sscore) {
super();
this.sid = sid;
this.sname = sname;
this.sscore = sscore;
}

// 先按分数从低到高排序，接着分数相同，按姓名排序，若姓名相同，按学号从小到大排序
@Override
public int compareTo(Student stu) {
int temp1 = Double.valueOf(this.sscore).compareTo(
Double.valueOf(stu.sscore));
if (0 == temp1) {
int temp2 = this.sname.compareTo(stu.sname);
if (0 == temp2) {
return Integer.valueOf(this.sid).compareTo(
Integer.valueOf(stu.sid));
}
return temp2;
}
return temp1;
}

}