rockpaperscissors

Rock-paper-scissors is a hand game played by two participants. Each player secretly selects one of three gestures and then reveals them simultaneously: rock (a clenched fist), paper (an open hand), or scissors (two extended fingers). The winner is determined by a simple cycle: rock beats scissors, scissors beats paper, and paper beats rock. If both players choose the same gesture, the round is a draw.

Play can be a quick single round or part of a longer match, such as best of three or best of five. In practice, players may try to read opponents' tendencies or establish patterns, but a strictly rational approach in a two-player setting is to randomize choices with equal probability, making opponents unable to gain a reliable edge.

Variants and related games have expanded the concept. The most well-known extension is Rock-Paper-Scissors-Lizard-Spock, which adds two gestures and a larger cycle of advantages, popularized in popular culture. The core mechanic — nondeterministic choice among several options with a fixed superiority relation — is the same in many other versions.

Historically, forms of the game appear in East Asia, with the Japanese version known as janken (often rendered jan-ken-pon in popular culture). The English name rock, paper, scissors is a translation of the local terms used in many languages. The game gained wide popularity in the 20th century and is frequently used as a simple decision tool or teaching aid in probability and game theory.

In game theory and computer science, rock-paper-scissors serves as a basic example of a nontransitive game and of mixed strategies. It is used to illustrate Nash equilibrium, strategic unpredictability, and as a testbed for algorithms that predict or compete against human play.