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	<title>If Chaos Were Organized &#187; hash tables</title>
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	<description>...then it'd be written about on the Internet</description>
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		<title>Pigeon Birthdays</title>
		<link>http://chaos.greenhead.com/archives/237</link>
		<comments>http://chaos.greenhead.com/archives/237#comments</comments>
		<pubDate>Mon, 10 Dec 2007 15:59:11 +0000</pubDate>
		<dc:creator>Weezel</dc:creator>
				<category><![CDATA[Geek]]></category>
		<category><![CDATA[birthday paradox]]></category>
		<category><![CDATA[coding]]></category>
		<category><![CDATA[cryptoanalysis]]></category>
		<category><![CDATA[hash tables]]></category>
		<category><![CDATA[intuition]]></category>
		<category><![CDATA[math]]></category>
		<category><![CDATA[pigeon hole]]></category>

		<guid isPermaLink="false">http://chaos.greenhead.com/archives/237</guid>
		<description><![CDATA[<p>The geek portion of my brain was catching up from some blog entries over the weekend and on Friday when I was out sick. In doing so, I came across <a href="http://www.codinghorror.com/blog/archives/001014.html"title="Coding Horror - Hashtables, Pigeonholes and Birthdays"  class="extlink">an entry at Coding Horror</a> which, in addition to discussing hash tables, discusses the <a href="http://en.wikipedia.org/wiki/Birthday_paradox"title="Wikipedia - Birthday Paradox"  class="extlink">Birthday Paradox</a>.</p>
<p><a href="http://chaos.greenhead.com/archives/237" class="more-link">Read more on Pigeon Birthdays&#8230;</a></p>
<!--<p class="tags">No Tags</p>--><!--<p class="tags">No Tags</p>-->]]></description>
			<content:encoded><![CDATA[<p>The geek portion of my brain was catching up from some blog entries over the weekend and on Friday when I was out sick. In doing so, I came across <a href="http://www.codinghorror.com/blog/archives/001014.html"title="Coding Horror - Hashtables, Pigeonholes and Birthdays"  class="extlink">an entry at Coding Horror</a> which, in addition to discussing hash tables, discusses the <a href="http://en.wikipedia.org/wiki/Birthday_paradox"title="Wikipedia - Birthday Paradox"  class="extlink">Birthday Paradox</a>.</p>
<p>&nbsp;</p>
<p>Now, I&#8217;d never heard of it before. But sure enough, when presented with the problem of &#8220;In a room of 23 people, what are the chances that any two would have the same birthday?&#8221; my mind took the exact same intuitive decision making steps that most folks would.</p>
<p>&nbsp;</p>
<p>( space left blank intentionally)</p>
<p>&nbsp;</p>
<p>&nbsp;</p>
<p>&nbsp;</p>
<p>&nbsp;</p>
<p>The answer is 50%.</p>
<p>&nbsp;</p>
<p>After reading&nbsp; <a href="http://betterexplained.com/articles/understanding-the-birthday-paradox/"title="Better Explained - Understanding the Birthday Paradox"  class="extlink">another math explanation</a> on why that&#8217;s true, I know that I understand it now. Sure, I might not be able to repeat (or fully understand) the math equations which generate the percentage, but I can identify the bottom line of understanding &#8212; when written in POE (plain ol&#8217; English):</p>
<p>&nbsp;</p>
<p>The actual birthday problem asks whether <i>any</i> of the 23 people have a matching birthday with <i>any</i> of the others — not one in particular. That means, you aren&#8217;t just taking any two people and comparing their birthdays, but simultaneously comparing all possible pairings of the group. </p>
<p>&nbsp;</p>
<p>It&#8217;s not the intuitive way to think of the problem. Your brain wants to tackle the problem it&#8217;s given of comparing two things, rather than the mathematical way which says &#8220;what are the chances that 23 people don&#8217;t share the same birthday&#8221;.</p>
<p>&nbsp;</p>
<div class="media">Now Playing: Steve Gibson with Leo Laporte &#8211; Security Now December 2007 &#8211; Security Now 121: Is Privacy Dead? </div>
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