考研机试 26.10进制 VS 2进制

import java.util.Scanner;
import java.math.BigInteger;

public class Main{
    
    public static void main(String[] args){
        
        Scanner in = new Scanner(System.in);
        
        //读取输入
        BigInteger n1 = new BigInteger(in.next());
        
        //转化为二进制
        String num2 = n1.toString(2);
        
        //逆序
        char[] ch = num2.toCharArray();
        for(int i = 0; i < ch.length / 2; i++){
            char temp = ch[i];
            ch[i] = ch[ch.length - i - 1];
            ch[ch.length - i - 1] = temp;
        }
        
        //转化为十进制
        String str1 = String.valueOf(ch);
        BigInteger n2 = new BigInteger(str1, 2);    //创建一个二进制的BigInteger对象
        String num10 = n2.toString(10);    //将二进制的BigInteger对象转化为十进制的字符串
        
        System.out.println(num10);
    }
}