java 大数类使用及案例

16年9月22日，感觉是时候复习算法，重新进军进军竞赛大军了。所有将会每天进行算法训练，但是不会放弃java软件设计和前端学习。
SO

正题来了，将昨天的大数类整理如下：

1. 定义大数变量：BigInteger x, BigInteger y;
2. 大数相加：x.add(y)
3. 大数相减：x.subtract(y)
4. 大数相乘：x.multiply(y)
5. 大数相除：x.divide(y)
6. 大数模运算：x.remainder(y)
7. 大数与大数之间赋值：x = y;
8. 大数与非大数之间赋值：x = BigIntteger.valueOf(int val)
9. 大数之间大小比较：x.compareTo(y)

更多函数请参考API

Example:

nyoj 45

import java.math.BigInteger;
import java.util.Scanner;


public class Main {


    public static void main(String[] args) {
        BigInteger res;
        int n, k;
        Scanner in = new Scanner(System.in);
        n = in.nextInt();

        for (int i = 0; i < n; i++)
        {
            res = BigInteger.valueOf(2);
            k  = in.nextInt();
            res = res.pow(2*k);
            res = res.subtract(BigInteger.ONE);
            res = res.divide(BigInteger.valueOf(3));
            System.out.println(res);
        }
    }
}

nyoj 28

import java.math.BigInteger;
import java.util.Scanner;


public class Main {


    public static void main(String[] args) {
        // TODO Auto-generated method stub
        BigInteger x, y;
        int n;
        Scanner in = new Scanner(System.in);
        n = in.nextInt();
        long start = System.currentTimeMillis();
        x = BigInteger.valueOf(1);
        for(int i = 1; i <= n; i++)
        {
            y =  BigInteger.valueOf(i);
            x = x.multiply(y);
        }
        System.out.println(x);
        long end = System.currentTimeMillis();
//      Float time = (float) ((end-start)/1000);
        long runTime = end - start;
        System.out.println(runTime);

    }


}

nyoj 73

import java.math.BigInteger;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        BigInteger x, y;
        Scanner in = new Scanner(System.in);
        x = in.nextBigInteger();
        y = in.nextBigInteger();
        while(!x.equals(BigInteger.ZERO) && !y.equals(BigInteger.ZERO))
        {
            if(x.compareTo(y) > 0) System.out.println("a>b");
            else if(x.compareTo(y) < 0) System.out.println("a);
            else System.out.println("a==b");
            x = in.nextBigInteger();
            y = in.nextBigInteger();

        }
    }
}

nyoj 103

import java.math.BigInteger;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        int t;
        BigInteger x, y, res;
        Scanner in = new Scanner(System.in);
        t = in.nextInt();
        for(int i = 1; i <= t; i++)
        {
            x = in.nextBigInteger();
            y = in.nextBigInteger();
            res = x.add(y);
            System.out.println("Case "+i+":");
            System.out.println(x + " + " + y + " = " +res);

        }
    }
}