RPS

Rock–Paper–Scissors (RPS) is a hand game played between two players who each simultaneously form one of three shapes: rock (a clenched fist), paper (an open hand), or scissors (a fist with the index and middle fingers extended). The outcome is determined by a simple cycle: rock beats scissors, scissors beats paper, and paper beats rock. If both players choose the same sign, the game is a draw.

RPS has historical roots in East Asia, with early references in China and Japan; it spread to Europe and the Americas in the 20th century and is now widely played as a casual pastime and as a simple decision mechanism in various contexts. Numerous regional variants and naming differences exist.

Strategies in RPS are often discussed in terms of probability and psychology. In theory, the optimal mixed strategy assigns equal probability to all three signs, making a player unpredictable. In practice, players exhibit biases (for example, favoring rock after losses) that can be exploited. Short sequences, patterns, and non-random play are common, and seasoned players may attempt to mislead or read an opponent's tendencies.

Beyond the basic game, there are many variants and extensions, such as Rock–Paper–Scissors–Lizard–Spock and other customized rule sets used in games or programming challenges. RPS is sometimes used in classrooms and AI demonstrations to illustrate probability, game theory, and decision-making.

RPS also appears in popular culture and competitions, from informal playground games to formal tournaments and online platforms that train models to predict opponent behavior or test simple strategy algorithms.