WealthSim.cs

static class Program
{
	// Make a random transaction between two people.
	static void randomTransaction( ref int to, ref int from )
	{
		const int transactionAmount = 5;
		int amount = Math.Min( transactionAmount, from );
		from -= amount;
		to += amount;
	}

	// Sample from sorted array at the specified location
	static int sample( this int[] arr, double where )
	{
		int idx = (int)Math.Round( where * ( arr.Length - 1 ) );
		return arr[ idx ];
	}

	static void Main()
	{
		// 100k people
		const int countPeople = 100000;
		// 1G random transactions
		const long countTransactions = 1000000000;

		// Initialize the array with equal number $100
		int[] arr = Enumerable.Repeat( 100, countPeople ).ToArray();
		Random random = new Random();

		// Run a large count of 100% fair random transactions
		for( long i = 0; i < countTransactions; i++ )
		{
			int a = random.Next( countPeople );
			int b = random.Next( countPeople );
			randomTransaction( ref arr[ a ], ref arr[ b ] );
		}

		// Print some wealth distribution figures
		Array.Sort( arr );
		IEnumerable<(string, double)> outputs()
		{
			yield return ("10%", 0.1);
			yield return ("20%", 0.2);
			yield return ("Median", 0.5);
			yield return ("80%", 0.8);
			yield return ("90%", 0.9);
			yield return ("99%", 0.99);
			yield return ("99.9%", 0.999);
		}
		foreach( (string label, double loc) in outputs() )
			Console.WriteLine( "{0}: ${1}", label, arr.sample( loc ) );

		// Print top 10 elements from the array
		var top10 = arr.Reverse().Take( 10 ).Select( a => $"${ a }" );
		Console.WriteLine( "Top 10 list: {0}", string.Join( ", ", top10 ) );
	}
}