BigInteger开方

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

public class 大数开方2 {

  public static void main(String[] args) {
    
    Scanner sc=new Scanner(System.in);
    
    for (int i = 0; i < 20; i++) {
      BigInteger n=BigInteger.valueOf(i);
      System.out.println(sqrt(n));
      
    }
    

  }

  private static BigInteger sqrt(BigInteger n) {
    BigInteger a;
    BigInteger b;
    
    //a为10的，n的长度除以二的，十次方
    a=BigInteger.TEN.pow((int)n.toString().length()/2);
    //b=n/a
    b=n.divide(a);
    
    //如果，a!=b,或者a和b的差相差不为0
    while(!(a.equals(b)||a.equals(b.add(new BigInteger("-1")))||b.equals(a.add(new BigInteger("-1"))))){
        
      //a=(a+b)/2
      a=a.add(b).divide(new BigInteger("2"));
      //b=n/a;
      b=n.divide(a);
    }
    //取a,b中较小的一个
    if (a.equals(b.add(new BigInteger("-1")))) {
      return a;
    }
    
    return b;
  }
}