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;
    }

}