With its acquisition of Hot Potato, Facebook Places follows the footsteps of Foursquare, Gowalla, et al. and makes its foray into location-aware social media. 

Since advertising is part of its core business model, adding the ability to make your posts geo-aware gives them a strategic advantage in this realm. 

Let’s say you’re checking out a new restaurant this evening.  If you enjoy the experience, the owners might offer you incentives to return if you checked-in with Facebook places.  Foursquare has already integrated these sort of incentives into its service. 

Foodies will love this.  Some time ago I started sharing photos of interesting meals (hat-tip to Jin Yang for the idea.)  No doubt, conversations sparked by the post have led to additional business for the restaurants whose food photographs well.

Unfortunately, Mark Zuckerburg’s egregious ineptitude with anything privacy related is glaring in the functionality built into Places, specifically its default settings.  While I’m fairly active on social media, some would say that I’m “Tweeting too hard.” Places really miffed me with its roll-out reminiscent of Google Buzz when it invades my private email with public status updates. 

The problem is easy enough to reproduce.

• Update to the latest version of Facebook Mobile on your device du jour.
• Check-in to any place using Facebook Places (a new icon with a map pin)
• Tag any of your friends, regardless of their privacy settings, and immediately, the internet knows exactly where you claim they are.

Why is this a problem?  This person didn’t give you permission to tell the world that they’re playing hooky from work to spend the day at the beach surfing with you.  I had a look on the friend’s settings who I tagged in a location and sure enough – the ability to tag them in Places was NOT enabled.  The circle of friends most people keep on Facebook is often much broader than anyone should feel comfortable sharing their location with on a regular basis.

Is this just a simple oversight?  I think not.  It is a shortcut taken to push the adoption of an add-on to an established service with an established user base at the expense and disregard of privacy of those users.

So I’m keeping my Foursquare account and will continue to share my location with friends I know and have explicitly granted access to my location.  Facebook’s offering needs some work before I’ll take a second look.

Google provides a Charting API with a host of useful charts. I spent a few minutes playing around with the map chart section to create a color-coded map of the states I have visited in the USA.

The Venn Diagram was an interesting option that I had not expected, but good stuff.

If you are building a dashboard, the Google-o-meter might come in handy

I find myself spending quite a bit of my spare time on Stackoverflow in recent weeks, and decided I wanted to display my current rep on my blog.  A few days ago I built a dynamically generated (and cached for 2 hours for traffic's sake) user ranking report, since my request for this on Uservoice was not approved.

HtmlAgilityPack has been my weapon of choice in recent days.  It was a good fit for this project and the end result looks like this:

And in case you might ask "Show me the code!" here you are.  Feel free to use it for your own project if you like.

          <%@
WebHandler Language="C#" Class="Badge" %> using System; using System.Web; publicclass Badge
: IHttpHandler { publicvoid ProcessRequest
(HttpContext context) { string includeLogo = !string.IsNullOrEmpty(context.Request.QueryString["useLogo"])
? 


context.Request.QueryString["useLogo"]
: string.Empty; string userId = !string.IsNullOrEmpty(context.Request.QueryString["userid"])
? 


context.Request.QueryString["userid"]
: "1551"; string jsMode = !string.IsNullOrEmpty(context.Request.QueryString["jsMode"])
? 


context.Request.QueryString["jsMode"]
: string.Empty;
PageRetriever pr =new PageRetriever("http://stackoverflow.com/users/"+ userId +"/");
pr.GetPage(); User userBadges = pr.ExtractBadge(); if (!string.IsNullOrEmpty(jsMode))
{ context.Response.ContentType ="text/javascript";
context.Response.Write("document.getElementById('stackoverflowRep').innerHTML
= '"); } else {
context.Response.ContentType ="text/html";
} if (!string.IsNullOrEmpty(includeLogo))
{ context.Response.Write("<div
style=\"height:40px\"><div style=\"float:left\"></div><div style=\"float:left;\">");

context.Response.Write(<img
src=\"http://www.chrisballance.com/so/resources/stackoverflow-logo-250.png\" />");
           }
context.Response.Write(userBadges.Rep); if (!string.IsNullOrEmpty(includeLogo))
{ context.Response.Write("<br
/><a href=\"http://stackoverflow.com/users/"); context.Response.Write(userId);
context.Response.Write("\">");
context.Response.Write(userBadges.Username); context.Response.Write("</a></div></div></div>");
} if (!string.IsNullOrEmpty(jsMode))
{ context.Response.Write("';\n");
} } publicbool IsReusable
{ get { returnfalse;
} } }
        

Since I could not find a chart of some sort showing current rankings on StackOverflow.com, I decided to roll my own.  The link that follows points to a static cached version of the page that will only update manually for now.  Enjoy, and feel free to give your feedback or suggestions for improvements.

Current StackOverflow.com Rankings

F# has 'easy button' for finding large primes!  29 lines of code!  Thanks to Chris Smith and his 'completely unique view' on the Sieve of Eratosthenes

          #light
open System.Collections.Generic open System let findPrimes = seq
{ yield 2 //2
is a known prime let knownComposites =new HashSet<int>() //Visit
each oddfor i in 3
.. 2 .. int 1E6 do//
Check known composites, if not present, it is prime. let found = knownComposites.Contains(i) if not
found then yield i //
Add all multiples of i to our sieve, starting //
at i and irecementing by i. dofor j in i
.. i .. int 1E6 do knownComposites.Add(j)
|> ignore } printfn "Here
are the first 10001 primes:" Seq.iter (fun p -> printf "\t%d" p)
(Seq.take 10001 findPrimes) Console.ReadKey(true)
        

Euler #6 is very straightforward. I was concerned about needing to work with numbers > 2^32, but this was not a factor. I initially set my bound to < max instead of <= max which threw my results off my a small margin (1-99 instead of 1-100). Runtime is < 1 ms, only ~2400 ticks.

          
            using System; using System.Diagnostics; namespace Euler6
{ class Program { staticvoid Main(string[]
args) { Stopwatch sw =new Stopwatch();
sw.Start(); long result = SumDifference(1,
100); sw.Stop(); Console.WriteLine("Runtime was "+ sw.ElapsedMilliseconds +"
ms"); Console.WriteLine("Runtime was "+ sw.ElapsedTicks +"
ticks"); Console.WriteLine("Sum difference is: "+ result);
Console.ReadLine(); } staticlong SumDifference(int begin, int end)
{ return SquareOfSums(begin, end) - SumOfSquares(begin,
end); } staticlong SumOfSquares(int begin, int end)
{ long returnValue = 0; for (int i = begin;
i <= end; i++) { returnValue += Convert.ToInt64(Math.Pow(i,2)); } return returnValue;
} staticlong SquareOfSums(int begin, int end)
{ long returnValue = 0; for (int i = begin;
i <= end; i++) { returnValue += i; } return Convert.ToInt64(Math.Pow(returnValue,
2)); } } }
        

          
            

            This one was elusively easy since I went with a simple brute-force
approach. Execution averages 1 second.
          
        

          
            using System; using System.Diagnostics; namespace Euler5
{ class Program { staticvoid Main(string[]
args) { Stopwatch sw =new Stopwatch();
sw.Start(); int lcm = FindLeastCommonMultiple();
sw.Stop(); Console.WriteLine("Runtime was "+ sw.ElapsedMilliseconds +"
ms"); Console.WriteLine("Runtime was "+ sw.ElapsedTicks +"
ticks"); Console.WriteLine("LCM is "+ lcm);
Console.ReadLine(); } privatestaticint FindLeastCommonMultiple()
{ for (int i = 2520;
i < int.MaxValue; i += 20) { if (IsDivisibleByRange(i,
1, 20)) return i; } return -1; } staticlong SmallestNumber()
{ return factorial(20); } staticlong factorial(long n)
{ long returnValue = 1; for (int i = 1;
i < n; i++) { returnValue *= i; } return returnValue; } staticbool IsDivisibleByRange(int num, int begin, int end)
{ for (int i = begin;
i <= end; i++) { if ((num % i)
!= 0) { returnfalse;
} } returntrue; } } }
        

There is certainly a more efficient algorithm solve Euler #4, but here is my solution.  Runtime averages around 500ms.

          
            using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Configuration; using System.Diagnostics; namespace Euler4
{ class Program
{ staticvoid Main(string[]
args) { long maxPal = 0; long iMax = 0; long jMax = 0;
Stopwatch sw =new Stopwatch();
sw.Start(); for (int i = 100;
i <= 999; i++) { for (int j = 100;
j <= 999; j++) { long curPal = (long)(i * j); if (CheckPallindrome(curPal))
{ if (curPal
> maxPal) { maxPal = curPal;
iMax = i;
jMax = j;
} } } } sw.Stop(); Console.WriteLine("Runtime
was "+ sw.ElapsedMilliseconds +"
ms"); Console.WriteLine("Runtime
was "+ sw.ElapsedTicks +"
ticks "); Console.WriteLine(iMax +"
x "+ jMax +"
= "+ maxPal);
Console.ReadLine(); } privatestaticbool CheckPallindrome(long input)
{ PallindromeChecker pc =new PallindromeChecker();
pc.Pal = input; return pc.IsPallindrome();
} } class PallindromeChecker
{ privatelong _pal; privatestring forward,
reverse; publiclong Pal
{ get { return _pal;
} set { _pal = value;
} } publicbool IsPallindrome()
{ GetReversedLong(); if (forward
== reverse) returntrue; returnfalse;
} privatevoid GetReversedLong()
{ forward = Convert.ToString(_pal);
StringBuilder temp2 =new StringBuilder(); char[]
arr =newchar[forward.Length - 1];
arr = forward.ToCharArray(); for (int i = forward.Length - 1;
i >= 0; i--) { temp2.Append(arr[i]); } reverse = temp2.ToString();
} } }
        

  In an effort to improve my algorithm design I have been working through some of the problems in the Euler Project and have found some of them to be quite intriguing.

Q: What is the largest prime factor of the number 600851475143 ?

I had the following issues to ponder:

• How to store and manipulate a 40-bit unsigned integer?
• To utilize recursion or not?
• Will the algorithm run in less than a minute?
  • If not, how do I make it more efficient?

The end result was simpler and much more performant than I had expected.  The 40-bit input fit into a long just fine.  Recursion was not necessary, and average runtimes are in the single digit millisecond range.  There was even an opportunity to use some very basic LINQ to retrieve the largest factor from the List

Here is the C# code:

            
              using System; using System.Collections; using System.Collections.Specialized; using System.Collections.Generic; using System.Linq; using System.Diagnostics; namespace Euler3
{ class PrimeFactorization
{ constlong ToFactor = 600851475143; publicstatic List<long>
theFactors =new List<long>(); staticvoid Main(string[]
args) { Stopwatch sw =new Stopwatch();
sw.Reset(); sw.Start(); Console.WriteLine("Highest
prime factor of ("+ ToFactor +")
is "+ HighestPrimeFactor(ToFactor));
sw.Stop(); Console.WriteLine("Factorization
algorithm runtime was: "+ sw.ElapsedTicks +"
ticks or "+ sw.ElapsedMilliseconds +"ms");
Console.ReadLine(); } privatestaticlong HighestPrimeFactor(long input)
{ bool searching =true; long highestFactor = 0; while (searching)
{ long factor = IsPrime(input); if (factor
!= -1)
{ theFactors.Add(factor); input = input / factor;
} if (factor
== -1) { theFactors.Add(input); highestFactor = theFactors.Max();
searching =false;
} } return highestFactor;
} privatestaticlong IsPrime(long input)
{ if ((input % 2)
== 0) { return 2;
} elseif ((input
== 1)) { return 1;
} else { long threshold = (Convert.ToInt64(Math.Sqrt(input))); long tryDivide = 3; while (tryDivide
< threshold) { if ((input % tryDivide)
== 0) { Console.WriteLine("Found
a factor: "+ tryDivide); return tryDivide;
} tryDivide += 2; } Console.WriteLine("Found
a factor: "+ input); return -1;
} } } }
          

            Output: