he was a boy she was a girl, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

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

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
           var list = new PersonList();
            list.AddBoy("Robert");
            list.AddBoy("John");
            list.AddBoy("Andrew");
            list.AddBoy("Tim");
            list.AddBoy("Fred");
            
            list.AddGirl("Amanda");
            list.AddGirl("Rachel");
            list.AddGirl("Deborah");
            list.AddGirl("Eileen");
            
            var groupOf4 = list.GetGroup(4);
            var groupOf5 = list.GetGroup(5);
            
            Console.WriteLine("4: " + String.Join(", ", groupOf4));
            Console.WriteLine("5: " + String.Join(", ", groupOf5));
        }
    }
    
    public class PersonList
    {
        private List<string> boys = new List<string>();
        private List<string> girls = new List<string>();
        
        public void AddBoy(string name)
        {
            boys.Add(name);
        }
        public void AddGirl(string name)
        {
            girls.Add(name);
        }   
        
        public IEnumerable<string> GetGroup(int size)
        {
            Shuffle(boys);
            Shuffle(girls);
            if((boys.Count + girls.Count) < size)
            {
                    throw new ArgumentException("Not enough people to satisfy group");
            }
            bool isBoy = rng.NextDouble() > 0.5;
            for(var i = 0;i<size;i++)
            {
                string next = "";
                if(isBoy)
                {
                    yield return PopBoy();
                }
                else
                {
                    yield return PopGirl();
                }
                isBoy = !isBoy;
            }
        }
        
        private string PopBoy()
        {
            if(boys.Count>0)
            {
                var name = boys[0];
                boys.RemoveAt(0);
                return name;
            }
            else
            {
                return PopGirl();
            }
        }
        private string PopGirl()
        {
            if(girls.Count>0)
            {
                var name = girls[0];
                girls.RemoveAt(0);
                return name;
            }
            else
            {
                return PopBoy();
            }
        }
        
        private static Random rng = new Random();

private static void Shuffle<T>(IList<T> list)  
        {  
            int n = list.Count;  
            while (n > 1) {  
                n--;  
                int k = rng.Next(n + 1);  
                T value = list[k];  
                list[k] = list[n];  
                list[n] = value;  
            }  
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,17 sec, absolute running time: 0,11 sec, cpu time: 0,09 sec, average memory usage: 16 Mb, average nr of threads: 3, absolute service time: 0,32 sec