题解 | #10进制 VS 2进制#

import java.util.Scanner;
import java.math.BigInteger;
// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        BigInteger a = in.nextBigInteger();
        String s = "";
        //转为二进制
        while(a!=BigInteger.valueOf(0)){
            s+=(a.mod(BigInteger.valueOf(2))).toString();
            a = a.divide(BigInteger.valueOf(2));
        }
        BigInteger weight =BigInteger.valueOf(1);
        a = BigInteger.valueOf(0);
        for(int i =s.length()-1;i>=0;i--){
            BigInteger temp = weight.multiply(BigInteger.valueOf(s.charAt(i)-'0'));
            a = a.add(temp);
            weight=weight.multiply(BigInteger.valueOf(2));            
        }
        //二进制转十进制
        System.out.println(a);
        
    }
}

真是jaja又vava啊