Java Fuck Bignumber

　为了熟悉java , 开一套poj大数处理的题来写.

-------------------------------------------------------------------

A:

　　（1）主要时间花在在处理输入上:

　　System.setIn(new FileInputStream("test.txt"));

　　相当于C++ 里面的　　　freopen("test.txt","r",stdin);

　　System.setOut(new FileOutputStream("ans.out"));

　　相当于C++里面的　　　 freopen("ans.out","w",stdout);

 

　　它应该要加在　　Scannercin = new Scanner (System.in); 的前面;

　　（2）cin.hashNext()  用来判断读入结束;

　　

　　文件输入输出:

　　BufferedReader rd = new BufferedReader(new FileReader("lottery.in"));

　　PrintWriter ot = new PrintWriter("lottery.out");

　　Scanner in = new Scanner(rd);

　　ot.println(ansBigInteger);

　　rd.close();

　　ot.close();

View Code

import java.io.*;

import java.math.*;

import java.util.Scanner;



public class Main 

{

    public static void main(String[] args) throws FileNotFoundException

    {

    //    System.setIn(new FileInputStream("test.txt"));

        Scanner cin = new Scanner (System.in);

        

        String str;

        BigDecimal ans,cur,eight;

        

        while (cin.hasNext())

        {

            eight = BigDecimal.valueOf(8);

            ans = BigDecimal.valueOf(0);

            cur = BigDecimal.valueOf(1);

            

            str = cin.nextLine();

            int pos = str.indexOf(".");

            BigDecimal tmp;

            for (int i = pos+1 ; i < str.length(); i++) 

            {

                cur = cur.divide(eight);

                tmp = BigDecimal.valueOf(str.charAt(i)-'0');

                

                tmp = tmp.multiply(cur);

                ans = ans.add(tmp);

            }

            System.out.println(str+" [8]"+" = "+ans+" [10]");

        }

        System.exit(0);

    }

}

 

B：

　　（1）void main要设成 static ， 于是所有要调用的函数都要用static修饰;

　　（2）BigIntegerans ans = BigInteger.valueOf(0);　　//可以得到一个值为int的 大数 ans

　　（3）大数ans的加/减/乘/除/都可以通过调用 ans.add(t) / add.subtract(t) / ans.multiply(t) /ans.divide(t) ； 参数t 必须也是大数;

View Code

 1 import java.io.FileInputStream;

 2 import java.io.FileNotFoundException;

 3 import java.math.BigInteger;

 4 import java.util.Arrays;

 5 import java.util.Scanner;

 6 

 7 

 8 public class Main 

 9 {

10     static private int maxn = 110;

11     static BigInteger dp[] = new BigInteger[maxn];

12     static BigInteger unvis = BigInteger.valueOf(-1);

13     

14     static private BigInteger getVal(int n) 

15     {

16         BigInteger ans;

17         ans = BigInteger.valueOf(n);

18         /*

19         for (int i=1 ; i<=n ; i++ )

20             ans = ans.multiply( BigInteger.valueOf(2) );

21         ans = ans.subtract(BigInteger.valueOf(1));*/

22         return ans;

23     }

24     static private BigInteger solv(int n) 

25     {

26         BigInteger ans = BigInteger.valueOf(0);

27         BigInteger tmp;

28         int i;

29         if (dp[n] != unvis) return dp[n];

30     //    System.out.println("n="+n);

31         for ( i=1 ; i<=n ; i++ )

32         {

33             tmp = getVal(i);

34             tmp = tmp.multiply(solv(n-i));

35     //        System.out.println("i="+i+" tmp="+tmp);

36             ans = ans.add(tmp);

37         }

38         return dp[n] = ans;

39     }

40     

41     static public void main(String[] args) throws FileNotFoundException 

42     {

43         Scanner cin = new Scanner(System.in);

44         int n;

45         while (cin.hasNext()) 

46         {

47             n = cin.nextInt();

48             Arrays.fill(dp, unvis);

49             dp[0] = BigInteger.valueOf(1);

50             System.out.println(solv(n));

51         }

52         System.exit(0);

53     }

54     

55 }

 

C:

　　（1）大数的进制转换:

　　 BigInter m = new BigInteger(st, base); // st以base进制转换成10进制

　　 类似的进制转换还有：

　 　String str = Integer.toString(num, base); // 把num当做10进制的数转成base进制的str(base <= 35).

　　 int num = Integer.parseInt(st, base); // 把st当做base进制，转成10进制的int

　　（2）关于字符串的操作:

　　 java的string是不可变类型,需要进行各种修改赋值操作的话,还是用stringBuffer比较方便

　　 相关资料

View Code

 1 import java.io.FileInputStream;

 2 import java.io.FileNotFoundException;

 3 import java.math.BigInteger;

 4 import java.util.Scanner;

 5 

 6 

 7 public class Main 

 8 {

 9     static BigInteger trans[] = new BigInteger[1000];

10     static char retrans[] = new char[1000];

11     static String TransToString(BigInteger ans,BigInteger base)

12     {

13         StringBuffer res = new StringBuffer();

14         BigInteger zero = BigInteger.valueOf(0);

15         if (ans.compareTo(zero) == 0)

16         {

17             res = res.append(0);

18             return res.toString();

19         }

20         while (ans.compareTo(zero) > 0)

21         {

22             int tmp = ans.mod(base).intValue();

23             res = res.append(retrans[tmp]);

24             ans = ans.divide(base);

25         }

26         res = res.reverse();

27         return res.toString();

28     }

29     static String getAns(String str,BigInteger base1,BigInteger base2)

30     {

31         int len = str.length(),i;

32         char[] ch = str.toCharArray();

33         BigInteger cur = BigInteger.valueOf(1);

34         BigInteger ans = BigInteger.valueOf(0);

35         for ( i=len-1 ; i>=1 ; i-- )

36         {

37             BigInteger tmp = trans[ch[i]].multiply(cur);

38             cur = cur.multiply(base1);

39             ans = ans.add(tmp);

40         }

41         String resString = TransToString(ans,base2);

42         return resString;

43     }

44     static void initTrans()

45     {

46         int idx=0;

47         char i;

48         for ( i='0' ; i<='9' ; i++ )    {trans[i] = BigInteger.valueOf(idx++);    retrans[idx-1]=i;}

49         for ( i='A' ; i<='Z' ; i++ )    {trans[i] = BigInteger.valueOf(idx++);    retrans[idx-1]=i;}

50         for ( i='a' ; i<='z' ; i++ )    {trans[i] = BigInteger.valueOf(idx++);    retrans[idx-1]=i;}

51     }

52     static public void main(String[] argStrings) throws FileNotFoundException

53     {

54 //        System.setIn(new FileInputStream("test.txt"));

55         Scanner cin = new Scanner(System.in);

56         String str;

57         initTrans();

58         int cas;

59         BigInteger base1,base2;

60         String ans;

61         cas = cin.nextInt();

62         for (int i = 0; i < cas; i++)    

63         {

64             base1 = cin.nextBigInteger();

65             base2 = cin.nextBigInteger();

66             str = cin.nextLine();

67             ans = getAns(str, base1, base2);

68             System.out.println(base1+str);

69             System.out.println(base2+" "+ans);

70             System.out.println();

71         }

72         System.exit(0);

73     }

74 }

 　　JAVA中的重定向: