.NET Fiddle

CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
    	var s = "<a href=\"/url?q=https://www.google.com/&sa=U&ved=0ahUKEwizwPy0yNHSAhXMDpAKHec7DAsQFgh6MA0&usg=AFQjCNEjJILXPMMCNAlz5MN1IIzjpr79tw\">";
    	var pattern = @"<a href=""/url\?q=(.*?)&";
    	var result = Regex.Match(s, pattern);
        if (result.Success)
        	Console.WriteLine(result.Groups[1].Value);
	}
}