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// Copyright 2019 Octavian Oncescu
use crate::graph::Graph;
use crate::vertex_id::VertexId;
use hashbrown::HashMap;
use std::sync::Arc;
#[derive(Debug)]
/// Depth-First Iterator
pub struct Dfs<'a, T> {
recursion_stack: Vec<Arc<VertexId>>,
color_map: HashMap<Arc<VertexId>, Color>,
roots_stack: Vec<Arc<VertexId>>,
iterable: &'a Graph<T>,
}
#[derive(Debug)]
enum Color {
White,
Grey,
Black,
}
impl<'a, T> Dfs<'a, T> {
pub fn new(graph: &'a Graph<T>) -> Dfs<'_, T> {
let mut roots_stack = Vec::with_capacity(graph.roots_count());
let color_map: HashMap<Arc<VertexId>, Color> = graph
.vertices()
.map(|v| (Arc::from(*v), Color::White))
.collect();
if graph.roots_count() == 0 && graph.vertex_count() != 0 {
// Pick random vertex as first root
for (random_vertex, _) in color_map.iter() {
roots_stack.push(random_vertex.clone());
break;
}
} else {
for v in graph.roots() {
roots_stack.push(Arc::from(*v));
}
}
Dfs {
color_map,
recursion_stack: Vec::with_capacity(graph.vertex_count()),
roots_stack,
iterable: graph,
}
}
/// Returns true if the iterated graph has a cycle.
pub fn is_cyclic(&mut self) -> bool {
while !self.roots_stack.is_empty() {
let root = self.roots_stack[self.roots_stack.len() - 1].clone();
// No vertices have been visited yet,
// so we begin from the current root.
if self.recursion_stack.is_empty() {
self.recursion_stack.push(root.clone());
self.color_map.insert(root.clone(), Color::Grey);
}
let mut current = self.recursion_stack.pop().unwrap();
loop {
if self.iterable.out_neighbors_count(current.as_ref()) == 0
&& !self.recursion_stack.is_empty()
{
// Mark as processed
self.color_map.insert(current.clone(), Color::Black);
// Set new current as popped value from recursion stack
current = self.recursion_stack.pop().unwrap();
continue;
}
break;
}
let mut all_are_black = true;
// Traverse current neighbors
for n in self.iterable.out_neighbors(current.as_ref()) {
let reference = Arc::from(*n);
if let Some(Color::White) = self.color_map.get(&reference) {
self.recursion_stack.push(current.clone());
self.recursion_stack.push(reference.clone());
self.color_map.insert(reference, Color::Grey);
all_are_black = false;
break;
}
// This means there is a cycle
if let Some(Color::Grey) = self.color_map.get(&reference) {
return true;
}
}
if all_are_black {
self.color_map.insert(current.clone(), Color::Black);
}
// Begin traversing from next root if the
// recursion stack is empty.
if self.recursion_stack.is_empty() {
self.roots_stack.pop();
}
}
false
}
}
impl<'a, T> Iterator for Dfs<'a, T> {
type Item = &'a VertexId;
fn next(&mut self) -> Option<Self::Item> {
while !self.roots_stack.is_empty() {
let root = self.roots_stack[self.roots_stack.len() - 1].clone();
// No vertices have been visited yet,
// so we begin from the current root.
if self.recursion_stack.is_empty() {
self.recursion_stack.push(root.clone());
self.color_map.insert(root.clone(), Color::Grey);
return self.iterable.fetch_id_ref(root.as_ref());
}
// Check if the topmost item on the recursion stack
// has outbound neighbors. If it does, we traverse
// them until we find one that is unvisited.
//
// If either the topmost item on the recursion stack
// doesn't have neighbors or all of its neighbors
// are visited, we pop it from the stack.
let mut current = self.recursion_stack.pop().unwrap();
loop {
if self.iterable.out_neighbors_count(current.as_ref()) == 0
&& !self.recursion_stack.is_empty()
{
// Mark as processed
self.color_map.insert(current.clone(), Color::Black);
// Pop from recursion stack
current = self.recursion_stack.pop().unwrap();
continue;
}
break;
}
let mut mark = true;
// Traverse current neighbors
for n in self.iterable.out_neighbors(current.as_ref()) {
let reference = Arc::from(*n);
if let Some(Color::White) = self.color_map.get(&reference) {
self.recursion_stack.push(current);
self.recursion_stack.push(reference.clone());
self.color_map.insert(reference, Color::Grey);
mark = false;
return Some(n);
}
}
if mark {
self.color_map.insert(current.clone(), Color::Black);
}
// Begin traversing from next root if the
// recursion stack is empty.
if self.recursion_stack.is_empty() {
self.roots_stack.pop();
}
}
None
}
}