java大数处理

比较两个数大小

import java.math.*;
import java.util.*;
public class Main {
        public static void main(String[] args) {
                Scanner cin = new Scanner(System.in);
                BigInteger c = new BigInteger("");
                while(cin.hasNext()){
                    BigInteger a = cin.nextBigInteger();
                    BigInteger b = cin.nextBigInteger();
                    if((a.compareTo(c)==) && (b.compareTo(c)==))
                        break;
                    int ok = a.compareTo(b);
                    if(ok==)
                        System.out.println("a==b");
                    else if(ok==-)
                        System.out.println("a<b");
                    else
                        System.out.println("a>b");
                }  

        }
}  

求一个数的阶乘

import java.math.*;
import java.util.*;
public class Main {
        public static void main(String[] args) {
                Scanner cin = new Scanner(System.in);
                while(cin.hasNext()){
                    int a = cin.nextInt();
                    BigInteger ans = new BigInteger("");
                    for(int i=;i<=a;i++)
                    {
                        BigInteger tmp = BigInteger.valueOf(i);
                        ans = ans.multiply(tmp);
                    }
                    System.out.println(ans);
                }
        }
}  

求a的b次方

import java.math.*;
import java.util.*;
public class Main {
        public static void main(String[] args) {
                Scanner cin = new Scanner(System.in);
                while(cin.hasNext()){
                    BigDecimal a = cin.nextBigDecimal();
                    BigDecimal ans = new BigDecimal("1.0");
                    int num = cin.nextInt();
                    ans = a.pow(num);
//                  for(int i=1;i<=num;i++)
//                  {
//                      ans = ans.multiply(a);
//                  }
                    String str = ans.stripTrailingZeros().toPlainString();
                    if(str.startsWith("")) //取掉前导0
                        str = str.substring();
                    System.out.println(str);
                }
        }
} 

斐波那契数列

F（0）=0，F（1）=1，F（n）=F(n-1)+F(n-2)（n≥2）

import java.math.*;
import java.util.*;
public class Main {
        public static void main(String[] args) {
                Scanner cin = new Scanner(System.in);
                BigInteger []a = new BigInteger[1005];
                a[1] = a[2] = new BigInteger("1");
                for(int i=3;i<=1001;i++)
                {
                    a[i] = a[i-1].add(a[i-2]);
                }
                int n,T;
                T = cin.nextInt();
                for(int cas = 1;cas<=T;cas++)
                {
                    n = cin.nextInt();
                    System.out.println(a[n]);
                }
        }
}