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:

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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);        }    }}

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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);    }}

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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<b");            else System.out.println("a==b");            x = in.nextBigInteger();            y = in.nextBigInteger();        }    }}

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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);        }    }}