java题目练手

大数阶乘

题目链接：http://acm.nyist.net/JudgeOnline/problem.php?pid=28

代码如下：

import java.io.*;
import java.math.BigInteger;
import java.util.*;

public class Main
{
    public static void main(String args[])
    {
        Scanner cin = new Scanner(System.in);
        int n = cin.nextInt();
        BigInteger ans = BigInteger.ONE;
        for(int i = 1; i <= n; ++i)
            ans = ans.multiply(BigInteger.valueOf(i));
        System.out.println(ans);
    }
}

棋盘覆盖

题目链接：http://acm.nyist.net/JudgeOnline/problem.php?pid=45

代码如下：

import java.math.BigInteger;
import java.util.*;
import java.io.*;

public class Main
{
    public static void main(String args[])
    {
        Scanner in = new Scanner(System.in);
        int test = in.nextInt();
        while(test-- > 0)
        {
            int n;
            n = in.nextInt();
            BigInteger a = new BigInteger("4");
            for(int i = 1; i < n; ++i)
                a = a.multiply(BigInteger.valueOf(4));
            System.out.println(a.subtract(BigInteger.valueOf(1)).divide(BigInteger.valueOf(3)));
        }
    }
}

比较大小

题目链接：http://acm.nyist.net/JudgeOnline/problem.php?pid=73

代码如下：

import java.io.*;
import java.math.BigInteger;
import java.util.*;

public class Main
{
    public static void main(String args[])
    {
        Scanner cin = new Scanner(System.in);
        while(cin.hasNext())
        {
            BigInteger a = cin.nextBigInteger();
            BigInteger b = cin.nextBigInteger();
            if(a.equals(BigInteger.ZERO) && b.equals(BigInteger.ZERO))
                break;
            int flag = a.compareTo(b);
            if(flag == -1)
                System.out.println("a<b");
            else if(flag == 0)
                System.out.println("a==b");
            else
                System.out.println("a>b");
        }
    }
}

大数加法

题目链接：http://acm.nyist.net/JudgeOnline/problem.php?pid=103

代码如下：

import java.math.BigInteger;
import java.util.*;
import java.io.*;

public class Main
{
    public static void main(String args[])
    {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        for(int i = 1; i <= n; ++i)
        {
            BigInteger a = in.nextBigInteger();
            BigInteger b = in.nextBigInteger();
            BigInteger ans = a.add(b);
            System.out.println("Case " + i + ":");
            System.out.println(a + " + " + b + " = " +ans);
        }
    }
}

递推求值

题目链接：http://acm.nyist.net/JudgeOnline/problem.php?pid=114

代码如下：

import java.io.*;
import java.math.BigInteger;
import java.util.*;

public class Main
{
    public static void main(String args[])
    {
        Scanner cin = new Scanner(System.in);
        BigInteger a[] = new BigInteger[100];
        while(cin.hasNext())
        {
            for(int i = 0; i <= 2; ++i)
                a[i] = cin.nextBigInteger();
            for(int i = 3; i <= 99; ++i)
                a[i] = a[i - 1].add(a[i - 2]).add(a[i - 3]);
            System.out.println(a[99]);
        }
    }
}

高精度幂

题目链接：http://acm.nyist.net/JudgeOnline/problem.php?pid=155

代码如下：

import java.io.*;
import java.math.BigDecimal;
import java.util.*;

public class Main
{
    public static void main(String args[])
    {
        Scanner cin = new Scanner(System.in);
        while(cin.hasNext())
        {
            BigDecimal ans = cin.nextBigDecimal();
            int n = cin.nextInt();
            String res = ans.pow(n).stripTrailingZeros().toPlainString(); //整数去掉小数点和后面的0
            if(res.startsWith("0")) //去掉前导0
            {
                res = res.substring(1);
            }
            System.out.println(res);
        }
    }
}