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;

    }



}