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("0");  
                while(cin.hasNext()){  
                    BigInteger a = cin.nextBigInteger();  
                    BigInteger b = cin.nextBigInteger();  
                    if((a.compareTo(c)==0) && (b.compareTo(c)==0))  
                        break;  
                    int ok = a.compareTo(b);  
                    if(ok==0)  
                        System.out.println("a==b");  
                    else if(ok==-1)  
                        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("1");  
                    for(int i=1;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("0")) //取掉前导0  
                        str = str.substring(1);  
                    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]);  
                }  
        }  
}