Exponentiation（POJ-1001） Java大数例题

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本文介绍了一个使用Java实现的精确计算方法，针对浮点数的n次方运算，确保结果既不采用科学计数法表示也不包含多余的前导或尾随零。

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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

Sample Output

548815620517731830194541.899025343415715973535967221869852721
.00000005148554641076956121994511276767154838481760200726351203835429763013462401
43992025569.928573701266488041146654993318703707511666295476720493953024
29448126.764121021618164430206909037173276672
90429072743629540498.107596019456651774561044010001
1.126825030131969720661201

计算浮点数的n次方，要求不用科学计数法，没有尾部以及开头零。

ps：我主要是用c++的，java很少用，用到的也只有大数，所以我觉得java到这再加上之前的那些函数就差不多了；

import java.util.*;
import java.math.*;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input=new Scanner(System.in);
		while(input.hasNext()){
			BigDecimal a=input.nextBigDecimal();  //大数类的double;
			int b=input.nextInt();
			a=a.pow(b);
			String ans=a.stripTrailingZeros().toPlainString();  //去掉尾部零，转换成非科学计数法字符串  
			if(ans.charAt(0)=='0'){  //如果以0开头  
				ans=ans.substring(1);  //返回以位置1开头的该字符串  
			}
			System.out.println(ans);
			
		}

	}

}