[置顶] 【POJ】1001 Exponentiation

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 R ⁿ 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

这道题是标准的大数运算，考察大数的幂操作，需要注意结果格式化输出。如果用C写就用字符数组存储数字，模拟手算过程，比较费事。

而POJ有Java编译器，所以关于大数运算的题目可以“投机取巧”的使用Java。Java的包提供了丰富的操作，关于大数运算，主要涉及以下类：

BigInteger java.math.BigInteger

BigDecimal java.math.BigDecimal

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

public class Main
{
	public static void main(String[] args)
	{
		Scanner input = new Scanner(System.in);
		while (input.hasNext())
		{
			BigDecimal r = input.nextBigDecimal().stripTrailingZeros();
			int n = input.nextInt();
			
			String temp = r.pow(n).toPlainString();
			String val = new String();
			
			// 去除小数点前的前导0
			int i = 0;
			for (; i<temp.length(); ++i)
				if (temp.charAt(i) != '0')
					break;
			val = temp.substring(i, temp.length());
			System.out.println(val);
		}
	}
}

最好使用Java语言尤其需要注意：

POJ提交的Java程序必须是一个单源文件，并且是一个以Main命名的类，中间的执行代码在静态的main函数中，否则会引起编译错误。