Question

How to calculate Sqrt of BigInteger in C#

Answer 1

using System;
using System.Numerics;
 
public class Program
{
    public static BigInteger Sqrt(BigInteger bi) {
        if (bi == 0) return 0;
       
		int length = Convert.ToInt32(Math.Ceiling(BigInteger.Log(bi, 10)));
        BigInteger root = BigInteger.One << (length / 2);
 
        while (!isSqrt(bi, root)) {
            root += bi / root;
            root /= 2;
        }
         
        return root;
    }
     
    private static Boolean isSqrt(BigInteger bi, BigInteger root) {
        BigInteger lowerBound = root * root;
        BigInteger upperBound = (root + 1) * (root + 1);
 
        return bi >= lowerBound && bi < upperBound;
    }
     
    public static void Main()
    {
        BigInteger bigInteger = BigInteger.Parse("58820136703657669922151936"); 
         
        try {
            Console.WriteLine("Sqrt: " + Sqrt(bigInteger));
        }
        catch (ArithmeticException e) {
            Console.WriteLine(e.Message);
        }
    }
}
 
// 7669428707775.9364176426041243971 
 
/*
run:
 
Sqrt: 7669428707775

 
*/

 

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