java BigInteger，BigDecimal学习

java里的BigInteger和BigDecimal是很好的东东，很大程度上把人从高精度的编码中解脱了出来。

相关博客：

BigInteger：

http://blog.csdn.net/thearcticocean/article/details/49280645

BigDecimal：

http://www.apihome.cn/api/java/BigDecimal.html

一些练习：

nyist 73 比大小

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

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

nyist 103 A+B Problem II

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

import java.util.*;
import java.math.BigInteger;
public class Main {
 public static void main(String[] args) {
        Scanner cin=new Scanner (System.in);
  int t,ca=1;
  t=cin.nextInt();
  while(t>0){
   t--;
   BigInteger a,b;
   a=cin.nextBigInteger();
   b=cin.nextBigInteger();
   System.out.printf("Case %d:\n",ca++);
   System.out.println(a+" + "+b+" = "+(a.add(b)));
  }
 }
}

51nod 1029 大数除法

http://www.51nod.com/onlineJudge/questionCode.html#!problemId=1029

import java.util.*;
import java.math.BigInteger;
public class Main {

 public static void main(String[] args) {
  BigInteger a,b;
  Scanner cin=new Scanner (System.in);
  while(cin.hasNext()){
   a=cin.nextBigInteger();
   b=cin.nextBigInteger();
   System.out.println(a.divide(b));
   System.out.println(a.remainder(b));
  }
 }
}

nyist 28 大数阶乘

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

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

}

51nod 1030 大数进制转换

http://www.51nod.com/onlineJudge/questionCode.html#!problemId=1030

import java.util.*;
import java.math.BigInteger;
public class Main{
 public static void main(String[] args) {
         String str="";
         Scanner cin=new Scanner (System.in);
         while(cin.hasNext()){
          str=cin.nextLine();
          String ans=new BigInteger(str,36).toString(10);
          System.out.println(ans);
         }
 }
}

nyist 114 某种序列

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

描述：数列A满足An = An-1 + An-2 + An-3, n >= 3。编写程序，给定A0, A1 和 A2, 计算A99

原来的思路：

  

发现反正涉及到大数，避开不了，那就用java大数水吧。

import java.util.*;
import java.math.BigInteger;
public class Main {

 public static void main(String[] args) {
  Scanner cin=new Scanner (System.in);
  BigInteger []a=new BigInteger [5];
  while(cin.hasNext()){
   a[0]=cin.nextBigInteger();
   a[1]=cin.nextBigInteger();
   a[2]=cin.nextBigInteger();
   for(int i=3;i<=99;i++){
    a[3]=a[2].add(a[1]);
    a[3]=a[3].add(a[0]);
    a[0]=a[1];
    a[1]=a[2];
    a[2]=a[3];
   }
   System.out.println(a[2]);
  }
 }
}

nyist 45 棋盘覆盖

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

分析：理性分析看不出来，直接找规律，

import java.util.*;
import java.math.BigInteger;
public class Main {
 public static void main(String[] args) {
  int m,k;
  Scanner sc=new Scanner (System.in);
  m=sc.nextInt();
  while(m>0){
   m--;
   BigInteger ans=BigInteger.ONE;
   k=sc.nextInt();
   for(int i=1;i<=k;i++){
    ans=ans.multiply(BigInteger.valueOf(4));
   }
   ans=ans.subtract(BigInteger.valueOf(1));
   ans=ans.divide(BigInteger.valueOf(3));
   System.out.println(ans);
  }
 }
}

做题过程中发现，用含有包语句的代码提交后出现RE，必须除去它。