Exponentiation（java 大实数）

http://acm.hdu.edu.cn/showproblem.php?pid=1063

Exponentiation

Time Limit: 2000/500 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 8076    Accepted Submission(s): 2279

Problem Description

Problems involving the computation of exact values of very large magnitude and precision are common. For example, the computation of the national debt is a taxing experience for many computer systems. 

This problem requires that you write a program to compute the exact value of Rⁿ where R is a real number ( 0.0 < R < 99.999 ) and n is an integer such that 0 < n <= 25. 

 

Input

The input will consist of a set of pairs of values for R and n. The R value will occupy columns 1 through 6, and the n value will be in columns 8 and 9.

 

Output

The output will consist of one line for each line of input giving the exact value of R^n. Leading zeros should be suppressed in the output. Insignificant trailing zeros must not be printed. Don't print the decimal point if the result is an integer.

 

Sample Input

95.123 12 0.4321 20 5.1234 15 6.7592 9 98.999 10 1.0100 12

 

Sample Output

548815620517731830194541.899025343415715973535967221869852721 .00000005148554641076956121994511276767154838481760200726351203835429763013462401 43992025569.928573701266488041146654993318703707511666295476720493953024 29448126.764121021618164430206909037173276672 90429072743629540498.107596019456651774561044010001 1.126825030131969720661201

import java.math.BigDecimal;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
    Scanner s = new Scanner(System.in);
    while(s.hasNext()){
        BigDecimal b = s.nextBigDecimal();
        BigDecimal ans = BigDecimal.valueOf(1);
        int n = s.nextInt();
        while(n-- > 0)
            ans = ans.multiply(b);
        String string = ans.stripTrailingZeros().toPlainString().toString();
        if(string.startsWith("0."))
            string = string.substring(1);
        System.out.println(string);
    }
        s.close();
    }
}

1、stripTrailingZeros() ，返回类型为BigDecimal的小于此数的但除去尾部的0的数值。

2、toPlainString()，返回BigDecimal类型的String类型字符串。

3、startsWith()，确定此实例的开头是否与指定的字符串匹配。

4、substring()，返回一个新的字符串，它是此字符串的一个子字符串。该子字符串始于指定索引处的字符，一直到此字符串末尾。

大家都知道JAVA的类一般都要带toString这个方法的，BigDecimal则有toString,toPlainString和toEngineeringString三种表示成字符串的方法，

下面是这三种方法各自的特点：

toString: using scientific notation if an exponent is needed;

toEngineeringString:using engineering notation if an exponent is needed.

toPlainString:without an exponent field.