HDU_1063_Exponentiation_大数

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原文链接：http://www.cnblogs.com/jasonlixuetao/p/5535253.html

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#java

本文介绍了一种使用Java实现的精确计算大数幂的方法。针对输入的实数R（0.0<R<99.999）和整数n（0<n≤25），程序能够准确计算并输出R^n的精确值，同时去除无效的前导零和尾随零。

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Exponentiation

Time Limit: 2000/500 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 8874 Accepted Submission(s): 2556

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

情不自禁的感叹：java大法好。

toString() 转成字符串，但数太大或太小时，用科学计数法。

toPlainString() 转成字符串，普通计数。

triptrailingzeros() 去掉最后面后缀0

substring() 取子串

import java.util.*;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.io.*;

public class Main {
        
    public static void main(String[] args) {
        BigDecimal a;
        int n;
        double r;
        Scanner in=new Scanner(System.in);
        while(in.hasNext())
        {
            r=in.nextDouble();
            n=in.nextInt();
            a=BigDecimal.valueOf(r);
            String s=a.pow(n).stripTrailingZeros().toPlainString();
            if("0".equals(s.substring(0,1))&&s.length()>1)
                System.out.println(s.substring(1));
            else
                System.out.println(s);
        }
}
}