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/* * Copyright (c) 2017, 2018, 2020 Frank Fischer <frank-fischer@shadow-soft.de> * * This program is free software: you can redistribute it and/or * modify it under the terms of the GNU General Public License as * published by the Free Software Foundation, either version 3 of the * License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/> */ //! Depth-first-search. //! //! # Example //! //! ``` //! use rs_graph::LinkedListGraph; //! use rs_graph::traits::*; //! use rs_graph::classes; //! use rs_graph::search::dfs; //! //! let g: LinkedListGraph = classes::peterson(); //! let mut cnt = 0; //! for (u, e) in dfs::start(g.neighbors(), g.id2node(0)) { //! assert_ne!(g.node_id(u), 0); //! cnt += 1; //! } //! assert_eq!(cnt, g.num_nodes() - 1); //! ``` use crate::adjacencies::Adjacencies; use crate::collections::{ItemMap, ItemStack}; use crate::traits::GraphType; use std::collections::HashMap; use std::hash::Hash; use std::marker::PhantomData; /// DFS iterator with default data structures. pub type DFSDefault<'a, A> = DFS<'a, A, HashMap<<A as GraphType<'a>>::Node, <A as GraphType<'a>>::Edge>, Vec<<A as Adjacencies<'a>>::Incidence>>; /// Start and return a DFS iterator using default data structures. /// /// This is a convenience wrapper around [`start_with_data`] using the default /// data structures returned by [`default_data`]. /// /// # Parameter /// - `adj`: adjacency information for the graph /// - `src`: the source node at which the search should start. pub fn start<'a, A>(adj: A, src: A::Node) -> DFSDefault<'a, A> where A: Adjacencies<'a>, A::Node: Hash, { start_with_data(adj, src, default_data()) } /// Start and return a DFS iterator with user defined data structures. /// /// The returned iterator traverses the edges in depth-first order. The /// iterator returns the next node and its incoming edge. /// /// Note that the start node is *not* returned by the iterator. /// /// The algorithm requires a pair `(M, S)` with `M` implementing [`ItemMap<Node, /// Edge>`][crate::collections::ItemMap], and `S` implementing /// [`ItemStack<_>`][crate::collections::ItemStack] as internal data /// structures. The map is used to store the last edge of the path from the /// source to each reachable node. The stack is used to handle the nodes in /// depth-first order. The data structures can be reused for multiple /// searches. /// /// # Parameter /// - `adj`: adjacency information for the graph /// - `src`: the source node at which the search should start. /// - `data`: the data structures used in the algorithm /// /// # Example /// /// ``` /// use rs_graph::LinkedListGraph; /// use rs_graph::traits::*; /// use rs_graph::classes; /// use rs_graph::search::dfs; /// use std::collections::HashMap; /// /// let g: LinkedListGraph = classes::peterson(); /// let mut cnt = 0; /// for (u, e) in dfs::start_with_data(g.neighbors(), g.id2node(0), /// (HashMap::new(), Vec::new())) /// { /// assert_ne!(g.node_id(u), 0); /// cnt += 1; /// } /// assert_eq!(cnt, g.num_nodes() - 1); /// ``` pub fn start_with_data<'a, A, S, St>(adj: A, src: A::Node, data: (S, St)) -> DFS<'a, A, S, St> where A: Adjacencies<'a>, S: ItemMap<A::Node, A::Edge>, St: ItemStack<A::Incidence>, { let (mut seen, mut stack) = data; seen.clear(); stack.clear(); if let Some(it) = adj.first(src) { stack.push(it); } DFS { adj, src, seen, stack, phantom: PhantomData, } } /// Return the default data structure to be used in the DFS. /// /// This is a [`HashMap`] and a [`Vec`]. pub fn default_data<N, E, I>() -> (HashMap<N, E>, Vec<I>) where N: Copy + Eq + Hash, { (HashMap::new(), Vec::new()) } pub struct DFS<'a, A, S, St> where A: Adjacencies<'a>, S: ItemMap<A::Node, A::Edge>, St: ItemStack<A::Incidence>, { adj: A, src: A::Node, seen: S, stack: St, phantom: PhantomData<&'a ()>, } impl<'a, A, S, St> Iterator for DFS<'a, A, S, St> where A: Adjacencies<'a>, S: ItemMap<A::Node, A::Edge>, St: ItemStack<A::Incidence>, { type Item = (A::Node, A::Edge); fn next(&mut self) -> Option<Self::Item> { while let Some(it) = self.stack.pop() { let (e, v) = self.adj.get(&it); if let Some(nxt) = self.adj.next(it) { self.stack.push(nxt); } if v != self.src && self.seen.insert(v, e) { if let Some(it) = self.adj.first(v) { self.stack.push(it); } return Some((v, e)); } } None } } impl<'a, A, S, St> DFS<'a, A, S, St> where A: Adjacencies<'a>, S: ItemMap<A::Node, A::Edge>, St: ItemStack<A::Incidence>, { /// Run the dfs completely. /// /// Note that this method may run forever on an infinite graph. pub fn run(&mut self) { while self.next().is_some() {} } /// Return the data structures used in the search. pub fn into_data(self) -> (S, St) { (self.seen, self.stack) } /// Return the incoming edge of a node. pub fn incoming_edge(&self, u: A::Node) -> Option<A::Edge> { self.seen.get(u).cloned() } }