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