Editing Rock paper scissors (section)

== Strategies ==
[[File:Roshambo-Laos.jpg|thumb|Children in Laos playing rock paper scissors]]
[[File:Roshambo-Myanmar.jpg|thumb|Children in Myanmar playing rock paper scissors]]
It is impossible to gain an advantage over an opponent that chooses their move [[Discrete uniform distribution|uniformly at random]]. However, it is possible to gain a significant advantage over a non-random player by predicting their move, which can be done by exploiting psychological effects or by analyzing statistical patterns of their past behavior.<ref name="rpscontest"/><ref name = "bbc rps">{{cite news |url=https://www.bbc.co.uk/news/science-environment-27228416 |title=How to win at rock–paper–scissors |first=James |last=Morgan |work=BBC News |publisher=BBC |date=2 May 2014 |access-date=2 May 2014 |archive-date=2 May 2014 |archive-url=https://web.archive.org/web/20140502080443/http://www.bbc.co.uk/news/science-environment-27228416 |url-status=live }}</ref><ref>{{cite news|title=Rock-Paper-Scissors: You vs. the Computer|url=https://www.nytimes.com/interactive/science/rock-paper-scissors.html|author1=Dance, Gabriel|author2=Jackson, Tom|name-list-style=amp|access-date=2011-06-15|date=2010-10-07|work=The New York Times|archive-date=2011-04-30|archive-url=https://web.archive.org/web/20110430004735/http://www.nytimes.com/interactive/science/rock-paper-scissors.html|url-status=live}}</ref> As a result, there have been programming competitions for [[algorithm]]s that play rock paper scissors.<ref name="rpscontest">{{cite web|title=Rock Paper Scissors Programming Competition|url=http://www.rpscontest.com/|author=Knoll, Byron|access-date=2011-06-15|archive-date=2019-04-10|archive-url=https://web.archive.org/web/20190410031615/http://www.rpscontest.com/|url-status=live}}</ref><ref name="roshambo1">{{cite web|title=First International RoShamBo Programming Competition|url=https://webdocs.cs.ualberta.ca/~darse/rsb-results1.html|access-date=2011-06-15|date=1999-10-01|archive-date=2011-08-10|archive-url=https://web.archive.org/web/20110810213237/http://webdocs.cs.ualberta.ca/~darse/rsb-results1.html|url-status=dead}}</ref><ref name="roshambo2">{{cite web|title=Second International RoShamBo Programming Competition|url=https://webdocs.cs.ualberta.ca/~darse/rsbpc.html|access-date=2011-06-15|date=2001-03-20|archive-date=2011-08-07|archive-url=https://web.archive.org/web/20110807090758/http://webdocs.cs.ualberta.ca/~darse/rsbpc.html|url-status=dead}}</ref>

During tournaments, players often prepare their sequence of three gestures prior to the tournament's commencement.<ref name="Lawrence Journal-World">Steve Vockrodt, [http://www2.ljworld.com/news/2007/apr/08/student_rivals_throw_down_rock_paper_scissors_tour/ "Student rivals throw down at rock, paper, scissors tournament"] {{Webarchive|url=https://web.archive.org/web/20070428114558/http://www2.ljworld.com/news/2007/apr/08/student_rivals_throw_down_rock_paper_scissors_tour/ |date=2007-04-28 }}, ''[[Lawrence Journal-World]]'', 8 April 2007. Retrieved 13 April 2007.</ref><ref name="Fox News">Michael Y. Park, [https://www.foxnews.com/story/rock-paper-scissors-the-sport "Rock, Paper, Scissors, the Sport"], ''[[Fox News Channel|Fox News]]'', 20 March 2006. Retrieved 13 April 2007.</ref> Some tournament players employ tactics to confuse or trick the other player into making an illegal move, resulting in a loss. One such tactic is to shout the name of one move before throwing another, in order to misdirect and confuse their opponent.{{citation needed|date=May 2022}}

The "rock" move, in particular, is notable in that it is typically represented by a closed fist—often identical to the fist made by players during the initial countdown. If a player is attempting to beat their opponent based on quickly reading their hand gesture as the players are making their moves, it is possible to determine if the opponent is about to throw "rock" based on their lack of hand movement, as both "scissors" and "paper" require the player to reposition their hand. This can likewise be used to deceive an anticipating opponent by keeping one's fist closed until the last possible moment, leading them to believe that one is about to throw "rock".{{Citation needed|date=July 2023}}

=== Algorithms ===
As a consequence of rock paper scissors programming contests, many strong algorithms have emerged.<ref name="rpscontest"/><ref name="roshambo1"/><ref name="roshambo2"/> For example, Iocaine Powder, which won the First International RoShamBo Programming Competition in 1999,<ref name="roshambo1"/> uses a heuristically designed compilation of strategies.<ref>{{cite web|title=Iocaine Powder Explained|url=http://www.ofb.net/~egnor/iocaine.html|author=Egnor, Dan|access-date=2011-06-15|date=1999-10-01|url-status=dead|archive-url=https://web.archive.org/web/20110723203327/http://www.ofb.net/~egnor/iocaine.html|archive-date=2011-07-23}}</ref> For each strategy it employs, it also has six metastrategies which defeat second-guessing, triple-guessing, as well as second-guessing the opponent, and so on. The optimal strategy or metastrategy is chosen based on past performance. The main strategies it employs are history matching, frequency analysis, and random guessing. Its strongest strategy, history matching, searches for a sequence in the past that matches the last few moves in order to predict the next move of the algorithm. In frequency analysis, the program simply identifies the most frequently played move. The random guess is a fallback method that is used to prevent a devastating loss in the event that the other strategies fail. There have since been some innovations, such as using multiple history-matching schemes that each match a different aspect of the history&nbsp;– for example, the opponent's moves, the program's own moves, or a combination of both.<ref name="werfer">{{cite web|title=Rock Paper Scissors Programming Competition entry: DNA werfer 5 L500|url=http://www.rpscontest.com/entry/109010|author=dllu|access-date=2011-06-15|date=2011-06-14|archive-date=2012-03-25|archive-url=https://web.archive.org/web/20120325184613/http://www.rpscontest.com/entry/109010|url-status=live}}</ref> There have also been other algorithms based on [[Markov chain]]s.<ref>{{cite web|title=Rock Paper Scissors Programming Competition entry: sixth-order markov chain|url=http://www.rpscontest.com/entry/34014|author=rfw|access-date=2011-06-15|date=2011-05-22|archive-date=2012-03-25|archive-url=https://web.archive.org/web/20120325184648/http://www.rpscontest.com/entry/34014|url-status=live}}</ref>

In 2012, researchers from the Ishikawa Watanabe Laboratory at the [[University of Tokyo]] created a robot hand that can play rock paper scissors with a 100% win rate against a human opponent. Using a high-speed camera the robot recognizes within one [[millisecond]] which shape the human hand is making, then produces the corresponding winning shape.<ref>{{cite news| url=https://www.theguardian.com/technology/video/2012/jun/27/rock-paper-scissors-robot-video | location=London | work=The Guardian | title=Rock-paper-scissors robot wins every time – video | date=2012-06-27}}</ref><ref>{{cite web | url = http://www.k2.t.u-tokyo.ac.jp/fusion/Janken/index-e.html | title = Janken (rock-paper-scissors) robot with 100% winning rate (human-machine cooperation system) | website = The University of Tokyo | access-date = 12 January 2018 | archive-date = 12 January 2018 | archive-url = https://web.archive.org/web/20180112100934/http://www.k2.t.u-tokyo.ac.jp/fusion/Janken/index-e.html | url-status = dead }}</ref>