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//! Submodule providing the `SingletonNodes` trait and its blanket
//! implementation, which provides a method to retrieve the singleton nodes from
//! a graph, which is a node with no predecessor and no successors edges.
use alloc::vec::Vec;
use super::node_classification::predecessor_successor_flags;
use crate::traits::MonoplexMonopartiteGraph;
/// Trait providing the `singleton_nodes` method, which returns the singleton
/// nodes of the graph. A singleton node is a node with no predecessors and no
/// successors.
pub trait SingletonNodes: MonoplexMonopartiteGraph {
/// Returns the singleton nodes of the graph.
///
/// # Examples
///
/// ```
/// use geometric_traits::{
/// impls::{SortedVec, SquareCSR2D},
/// prelude::*,
/// traits::{EdgesBuilder, VocabularyBuilder},
/// };
///
/// let nodes: Vec<usize> = vec![0, 1, 2, 3];
/// let edges: Vec<(usize, usize)> = vec![(0, 1)];
/// let nodes: SortedVec<usize> = GenericVocabularyBuilder::default()
/// .expected_number_of_symbols(nodes.len())
/// .symbols(nodes.into_iter().enumerate())
/// .build()
/// .unwrap();
/// let edges: SquareCSR2D<_> = DiEdgesBuilder::default()
/// .expected_number_of_edges(edges.len())
/// .expected_shape(nodes.len())
/// .edges(edges.into_iter())
/// .build()
/// .unwrap();
/// let graph: DiGraph<usize> = DiGraph::from((nodes, edges));
///
/// // Node 2 and 3 are singleton nodes because they have no incoming or outgoing edges.
/// assert_eq!(graph.singleton_nodes(), vec![2, 3]);
/// ```
#[inline]
fn singleton_nodes(&self) -> Vec<Self::NodeId> {
let (has_predecessor, has_successor) = predecessor_successor_flags(self);
self.node_ids()
.zip(has_predecessor.into_iter().zip(has_successor))
.filter_map(|(node, (has_predecessor, has_successor))| {
(!has_predecessor && !has_successor).then_some(node)
})
.collect()
}
}
impl<G: MonoplexMonopartiteGraph + ?Sized> SingletonNodes for G {}