ddo 2.0.0

// Copyright 2020 Xavier Gillard
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal in
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// the Software, and to permit persons to whom the Software is furnished to do so,
// subject to the following conditions:
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// FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
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use crate::SubProblem;


/// This trait abstracts away the implementation details of the solver fringe.
/// That is, a Fringe represents the global priority queue which stores all 
/// the nodes remaining to explore.
pub trait Fringe {
    type State;

    /// This is how you push a node onto the fringe.
    fn push(&mut self, node: SubProblem<Self::State>);
    /// This method yields the most promising node from the fringe.
    /// # Note:
    /// The solvers rely on the assumption that a fringe will pop nodes in
    /// descending upper bound order. Hence, it is a requirement for any fringe
    /// implementation to enforce that requirement.
    fn pop(&mut self) -> Option<SubProblem<Self::State>>;
    /// This method clears the fringe: it removes all nodes from the queue.
    fn clear(&mut self);
    /// Yields the length of the queue.
    fn len(&self) -> usize;
    /// Returns true iff the fringe is empty (len == 0)
    fn is_empty(&self) -> bool {
        self.len() == 0
    }
}