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use std::slice;
/// A sparse set used for representing ordered NFA states.
///
/// This supports constant time addition and membership testing. Clearing an
/// entire set can also be done in constant time. Iteration yields elements
/// in the order in which they were inserted.
///
/// The data structure is based on: https://research.swtch.com/sparse
/// Note though that we don't actually use uninitialized memory. We generally
/// reuse sparse sets, so the initial allocation cost is bareable. However, its
/// other properties listed above are extremely useful.
#[derive(Clone, Debug)]
pub struct SparseSet {
/// Dense contains the instruction pointers in the order in which they
/// were inserted.
dense: Vec<usize>,
/// Sparse maps instruction pointers to their location in dense.
///
/// An instruction pointer is in the set if and only if
/// sparse[ip] < dense.len() && ip == dense[sparse[ip]].
sparse: Box<[usize]>,
}
impl SparseSet {
pub fn new(size: usize) -> SparseSet {
SparseSet {
dense: Vec::with_capacity(size),
sparse: vec![0; size].into_boxed_slice(),
}
}
pub fn len(&self) -> usize {
self.dense.len()
}
pub fn insert(&mut self, value: usize) {
let i = self.len();
assert!(i < self.dense.capacity());
self.dense.push(value);
self.sparse[value] = i;
}
pub fn contains(&self, value: usize) -> bool {
let i = self.sparse[value];
self.dense.get(i) == Some(&value)
}
pub fn clear(&mut self) {
self.dense.clear();
}
}
impl<'a> IntoIterator for &'a SparseSet {
type Item = &'a usize;
type IntoIter = slice::Iter<'a, usize>;
fn into_iter(self) -> Self::IntoIter {
self.dense.iter()
}
}
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