Shuffle Visualizer: Visual sanity-check for randomness in deck-shuffling algorithms (C#/ASP.NET WebForms version)

## TestShuffle.aspx
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="TestShuffle.aspx.cs" Inherits="TestShuffle" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Test shuffle</title>

    <style>
        body {
           font-family:Verdana;
           font-size:9px;
        }
        td {
           font-size:1px;
           width:12px;
           height:12px;
        }
    </style>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Literal ID="ltGraph" runat="server"></asp:Literal>
    </div>
    </form>
</body>
</html>

## TestShuffle.aspx.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Text;
using System.Diagnostics;

public partial class TestShuffle : System.Web.UI.Page
{
    protected int[] initDeck()
    {
        int[] deck = new int[52];

        for (int i = 0; i < 52; i++)
            deck[i] = i;

        return deck;
    }
    protected void test(int[] deck, Action<int[]> shuffle)
    {
        shuffle(deck);

        //error checking: check for illegal cards
        var outOfBounds = (from card in deck
                           where card < 0 || card > 51
                           select card).Distinct();

        if (outOfBounds.Count() > 0)
        {
            string errors = string.Join(", ", outOfBounds.Select(r => r.ToString()).ToArray());
            throw new Exception("Deck contains illegal cards: " + errors);
        }

        //error checking: check for duplicates
        var failCount = (from card in deck
                         where deck.Count(c => c == card) != 1
                         orderby card
                         select card).Distinct();

        if (failCount.Count() > 0)
        {
            string errors = string.Join(", ", failCount.Select(r => r.ToString()).ToArray());
            throw new Exception("Deck doesn't contain exactly 1 of each card: " + errors);
        }
    }

    int[,] hits { get; set; }
    void initHits()
    {
        hits = new int[52, 52];

        for (int i = 0; i < 52; i++)
        {
            for (int j = 0; j < 52; j++)
            {
                hits[i, j] = 0;
            }
        }
    }

    void plotHits(int[] deck)
    {
        for (int i = 0; i < deck.Length; i++)
        {
            hits[i, deck[i]]++;
        }
    }

    string hitsTable(bool grayscale = false)
    {
        StringBuilder sbTop = new StringBuilder("<table border='0' cellpadding='0' cellspacing='0'><tr><th>&nbsp;</th>");
        StringBuilder sbRows = new StringBuilder();

        for (int i = 0; i < 52; i++)
        {
            sbTop.AppendFormat("<th>{0}</th>", i);
            sbRows.AppendFormat("<tr><th>{0}</th>", i);

            for (int j = 0; j < 52; j++)
            {
                if (grayscale)
                {
                    var amplitude = hits[i, j] % 256;
                    sbRows.AppendFormat("<td style='background-color:rgb({0},{0},{0});'>&nbsp;</td>", amplitude);
                }
                else
                {
                    var amplitude = (int)Math.Pow(hits[i, j], 3);
                    sbRows.AppendFormat("<td style='background-color:#{0:x6};'>&nbsp;</td>", amplitude % 0x1000000);
                }
            }

            sbRows.AppendLine("</tr>");
        }

        sbTop.AppendLine("</tr>");
        return sbTop.AppendLine(sbRows.ToString()).AppendLine("</table>").ToString();
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        StringBuilder sb = new StringBuilder();

        var methods = new Action<int[]>[] { Shuffle.shuffle /*, Shuffle.shuffle2, etc. */ };
        int reps = 19000;

        foreach (Action<int[]> method in methods)
        {
            initHits();

            for (int i = 0; i < reps; i++)
            {
                var deck = initDeck();
                test(deck, method);
                plotHits(deck);
            }

            sb.AppendFormat(@"<div style='float:left;padding-left:10px;'><h2>{0}:</h2> {1}<br/></div>", method.Method.Name, hitsTable(true));
        }

        ltGraph.Text = sb.ToString();
    }
}