POJ1001 Exponentiation

以你之姓@ 2021-09-26 07:20 380阅读 0赞

**题目描述**  
总时间限制: 500ms 内存限制: 65536kB  
**描述**  
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 Rnwhere R is a real number ( 0.0 < R < 99.999 ) and n is an integer such that 0 < n <= 25.  
**输入**  
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.  
**输出**  
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.  
**样例输入**  
95.123 12  
0.4321 20  
5.1234 15  
6.7592 9  
98.999 10  
1.0100 12  
**样例输出**  
548815620517731830194541.899025343415715973535967221869852721  
.00000005148554641076956121994511276767154838481760200726351203835429763013462401  
43992025569.928573701266488041146654993318703707511666295476720493953024  
29448126.764121021618164430206909037173276672  
90429072743629540498.107596019456651774561044010001  
1.126825030131969720661201  
**题目分析：**  
此处要求得是R^n，使用double型容易发生溢出，考虑到Java提供的BigDecimal，使用Java自带的大数幂运算。同时，java的BigDecimal提供了stripTrailingZeros()方法可以去除大数末尾的0。

*  大数的toPlainString()方法 VS toString()方法：  
    toPlainString可以输出数值，而toString()方法则会使其变为科学计数法输出。

**代码如下**

import java.math.BigDecimal;
    import java.util.Scanner;
    
    public class Exponentiation {
    
        public static void main(String[] args) {
            // TODO Auto-generated method stub
            Scanner scanner = new Scanner(System.in);
            BigDecimal R;
            int n;
            while (scanner.hasNext()) {
                R= scanner.nextBigDecimal();
                n = scanner.nextInt();
                R = R.pow(n);
                String str = R.stripTrailingZeros().toPlainString();
                if (str.startsWith("0."))
                    str = str.substring(1);
                System.out.println(str);
            }
    
        }
    }