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//! Authors: Maurice Laveaux and Sjef van Loo
use core::fmt;
use crate::Priority;
/// The two players in a parity game.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum Player {
Even,
Odd,
}
impl Player {
/// Constructs a player from its index. This can be used in algorithms where
/// we have a 2-array, and 0 is Even and 1 is Odd.
pub fn from_index(index: u8) -> Self {
Self::try_from_index(index).unwrap_or_else(|| panic!("Invalid player index {}", index))
/// Constructs a player from its index, returning `None` for any value other
/// than 0 (Even) or 1 (Odd). Use this when the index comes from untrusted
/// input that should be reported as a recoverable error.
pub fn try_from_index(index: u8) -> Option<Self> {
match index {
0 => Some(Player::Even),
1 => Some(Player::Odd),
_ => None,
/// Constructs a player from a priority.
pub fn from_priority(priority: Priority) -> Self {
if priority.value().is_multiple_of(2) {
Player::Even
} else {
Player::Odd
/// Returns the index of the player, the inverse of [Self::from_index].
pub fn to_index(&self) -> usize {
match self {
Player::Even => 0,
Player::Odd => 1,
/// Returns the opponent of the current player.
pub fn opponent(&self) -> Self {
Player::Even => Player::Odd,
Player::Odd => Player::Even,
/// Returns the string representation of the solution for this player.
pub fn solution(&self) -> &'static str {
Player::Even => "true",
Player::Odd => "false",
impl fmt::Display for Player {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
Player::Even => write!(f, "even"),
Player::Odd => write!(f, "odd"),