Finite state machines
Abstract computational models with finite states, transitions triggered by input symbols, and optional output. Finite state machines model systems with sequential behavior like controllers and protocol parsing. Deterministic finite automata (DFA) have unique transitions per state-input pair. Non-deterministic finite automata (NFA) allow multiple or missing transitions.
Real World
London Underground ticket barriers use a finite state machine: states include 'locked' and 'unlocked', with transitions triggered by a valid Oyster card tap or a passenger walking through.
Exam Focus
When drawing state diagrams, always label the start state with an arrow and double-circle all accepting states.
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