1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440

use {Incoming};
use super::{IntoNeighbors, IntoNeighborsDirected, Visitable, VisitMap};
use super::{GraphRef, Reversed, IntoNodeIdentifiers};
use std::collections::VecDeque;

/// Visit nodes of a graph in a depth-first-search (DFS) emitting nodes in
/// preorder (when they are first discovered).
///
/// The traversal starts at a given node and only traverses nodes reachable
/// from it.
///
/// `Dfs` is not recursive.
///
/// `Dfs` does not itself borrow the graph, and because of this you can run
/// a traversal over a graph while still retaining mutable access to it, if you
/// use it like the following example:
///
/// ```
/// use petgraph::Graph;
/// use petgraph::visit::Dfs;
///
/// let mut graph = Graph::<_,()>::new();
/// let a = graph.add_node(0);
///
/// let mut dfs = Dfs::new(&graph, a);
/// while let Some(nx) = dfs.next(&graph) {
///     // we can access `graph` mutably here still
///     graph[nx] += 1;
/// }
///
/// assert_eq!(graph[a], 1);
/// ```
///
/// **Note:** The algorithm may not behave correctly if nodes are removed
/// during iteration. It may not necessarily visit added nodes or edges.
#[derive(Clone, Debug)]
pub struct Dfs<N, VM> {
    /// The stack of nodes to visit
    pub stack: Vec<N>,
    /// The map of discovered nodes
    pub discovered: VM,
}

impl<N, VM> Dfs<N, VM>
    where N: Copy + PartialEq,
          VM: VisitMap<N>,
{
    /// Create a new **Dfs**, using the graph's visitor map, and put **start**
    /// in the stack of nodes to visit.
    pub fn new<G>(graph: G, start: N) -> Self
        where G: GraphRef + Visitable<NodeId=N, Map=VM>
    {
        let mut dfs = Dfs::empty(graph);
        dfs.move_to(start);
        dfs
    }

    /// Create a `Dfs` from a vector and a visit map
    pub fn from_parts(stack: Vec<N>, discovered: VM) -> Self {
        Dfs {
            stack: stack,
            discovered: discovered,
        }
    }

    /// Clear the visit state
    pub fn reset<G>(&mut self, graph: G)
        where G: GraphRef + Visitable<NodeId=N, Map=VM>
    {
        graph.reset_map(&mut self.discovered);
        self.stack.clear();
    }

    /// Create a new **Dfs** using the graph's visitor map, and no stack.
    pub fn empty<G>(graph: G) -> Self
        where G: GraphRef + Visitable<NodeId=N, Map=VM>
    {
        Dfs {
            stack: Vec::new(),
            discovered: graph.visit_map(),
        }
    }

    /// Keep the discovered map, but clear the visit stack and restart
    /// the dfs from a particular node.
    pub fn move_to(&mut self, start: N)
    {
        self.discovered.visit(start);
        self.stack.clear();
        self.stack.push(start);
    }

    /// Return the next node in the dfs, or **None** if the traversal is done.
    pub fn next<G>(&mut self, graph: G) -> Option<N>
        where G: IntoNeighbors<NodeId=N>,
    {
        while let Some(node) = self.stack.pop() {
            for succ in graph.neighbors(node) {
                if self.discovered.visit(succ) {
                    self.stack.push(succ);
                }
            }

            return Some(node);
        }
        None
    }
}

/// Visit nodes in a depth-first-search (DFS) emitting nodes in postorder
/// (each node after all its decendants have been emitted).
///
/// `DfsPostOrder` is not recursive.
///
/// The traversal starts at a given node and only traverses nodes reachable
/// from it.
#[derive(Clone, Debug)]
pub struct DfsPostOrder<N, VM> {
    /// The stack of nodes to visit
    pub stack: Vec<N>,
    /// The map of discovered nodes
    pub discovered: VM,
    /// The map of finished nodes
    pub finished: VM,
}

impl<N, VM> DfsPostOrder<N, VM>
    where N: Copy + PartialEq,
          VM: VisitMap<N>,
{
    /// Create a new `DfsPostOrder` using the graph's visitor map, and put
    /// `start` in the stack of nodes to visit.
    pub fn new<G>(graph: G, start: N) -> Self
        where G: GraphRef + Visitable<NodeId=N, Map=VM>
    {
        let mut dfs = Self::empty(graph);
        dfs.move_to(start);
        dfs
    }

    /// Create a new `DfsPostOrder` using the graph's visitor map, and no stack.
    pub fn empty<G>(graph: G) -> Self
        where G: GraphRef + Visitable<NodeId=N, Map=VM>
    {
        DfsPostOrder {
            stack: Vec::new(),
            discovered: graph.visit_map(),
            finished: graph.visit_map(),
        }
    }

    /// Clear the visit state
    pub fn reset<G>(&mut self, graph: G)
        where G: GraphRef + Visitable<NodeId=N, Map=VM>
    {
        graph.reset_map(&mut self.discovered);
        graph.reset_map(&mut self.finished);
        self.stack.clear();
    }

    /// Keep the discovered and finished map, but clear the visit stack and restart
    /// the dfs from a particular node.
    pub fn move_to(&mut self, start: N)
    {
        self.stack.clear();
        self.stack.push(start);
    }

    /// Return the next node in the traversal, or `None` if the traversal is done.
    pub fn next<G>(&mut self, graph: G) -> Option<N>
        where G: IntoNeighbors<NodeId=N>,
    {
        while let Some(&nx) = self.stack.last() {
            if self.discovered.visit(nx) {
                // First time visiting `nx`: Push neighbors, don't pop `nx`
                for succ in graph.neighbors(nx) {
                    if !self.discovered.is_visited(&succ) {
                        self.stack.push(succ);
                    }
                }
            } else {
                self.stack.pop();
                if self.finished.visit(nx) {
                    // Second time: All reachable nodes must have been finished
                    return Some(nx);
                }
            }
        }
        None
    }
}

/// A breadth first search (BFS) of a graph.
///
/// The traversal starts at a given node and only traverses nodes reachable
/// from it.
///
/// `Bfs` is not recursive.
///
/// `Bfs` does not itself borrow the graph, and because of this you can run
/// a traversal over a graph while still retaining mutable access to it, if you
/// use it like the following example:
///
/// ```
/// use petgraph::Graph;
/// use petgraph::visit::Bfs;
///
/// let mut graph = Graph::<_,()>::new();
/// let a = graph.add_node(0);
///
/// let mut bfs = Bfs::new(&graph, a);
/// while let Some(nx) = bfs.next(&graph) {
///     // we can access `graph` mutably here still
///     graph[nx] += 1;
/// }
///
/// assert_eq!(graph[a], 1);
/// ```
///
/// **Note:** The algorithm may not behave correctly if nodes are removed
/// during iteration. It may not necessarily visit added nodes or edges.
#[derive(Clone)]
pub struct Bfs<N, VM> {
    /// The queue of nodes to visit
    pub stack: VecDeque<N>,
    /// The map of discovered nodes
    pub discovered: VM,
}

impl<N, VM> Bfs<N, VM>
    where N: Copy + PartialEq,
          VM: VisitMap<N>,
{
    /// Create a new **Bfs**, using the graph's visitor map, and put **start**
    /// in the stack of nodes to visit.
    pub fn new<G>(graph: G, start: N) -> Self
        where G: GraphRef + Visitable<NodeId=N, Map=VM>
    {
        let mut discovered = graph.visit_map();
        discovered.visit(start);
        let mut stack = VecDeque::new();
        stack.push_front(start);
        Bfs {
            stack: stack,
            discovered: discovered,
        }
    }

    /// Return the next node in the bfs, or **None** if the traversal is done.
    pub fn next<G>(&mut self, graph: G) -> Option<N>
        where G: IntoNeighbors<NodeId=N>
    {
        while let Some(node) = self.stack.pop_front() {
            for succ in graph.neighbors(node) {
                if self.discovered.visit(succ) {
                    self.stack.push_back(succ);
                }
            }

            return Some(node);
        }
        None
    }

}

/// A topological order traversal for a graph.
///
/// **Note** that `Topo` only visits nodes that are not part of cycles,
/// i.e. nodes in a true DAG. Use other visitors like `DfsPostOrder` or
/// algorithms like kosaraju_scc to handle graphs with possible cycles.
#[derive(Clone)]
pub struct Topo<N, VM> {
    tovisit: Vec<N>,
    ordered: VM,
}

impl<N, VM> Topo<N, VM>
    where N: Copy + PartialEq,
          VM: VisitMap<N>,
{
    /// Create a new `Topo`, using the graph's visitor map, and put all
    /// initial nodes in the to visit list.
    pub fn new<G>(graph: G) -> Self
        where G: IntoNodeIdentifiers + IntoNeighborsDirected + Visitable<NodeId=N, Map=VM>,
    {
        let mut topo = Self::empty(graph);
        topo.extend_with_initials(graph);
        topo
    }

    fn extend_with_initials<G>(&mut self, g: G)
        where G: IntoNodeIdentifiers + IntoNeighborsDirected<NodeId=N>,
    {
        // find all initial nodes (nodes without incoming edges)
        self.tovisit.extend(g.node_identifiers()
                             .filter(move |&a| g.neighbors_directed(a, Incoming).next().is_none()));
    }

    /* Private until it has a use */
    /// Create a new `Topo`, using the graph's visitor map with *no* starting
    /// index specified.
    fn empty<G>(graph: G) -> Self
        where G: GraphRef + Visitable<NodeId=N, Map=VM>
    {
        Topo {
            ordered: graph.visit_map(),
            tovisit: Vec::new(),
        }
    }

    /// Clear visited state, and put all initial nodes in the to visit list.
    pub fn reset<G>(&mut self, graph: G)
        where G: IntoNodeIdentifiers + IntoNeighborsDirected + Visitable<NodeId=N, Map=VM>,
    {
        graph.reset_map(&mut self.ordered);
        self.tovisit.clear();
        self.extend_with_initials(graph);
    }

    /// Return the next node in the current topological order traversal, or
    /// `None` if the traversal is at the end.
    ///
    /// *Note:* The graph may not have a complete topological order, and the only
    /// way to know is to run the whole traversal and make sure it visits every node.
    pub fn next<G>(&mut self, g: G) -> Option<N>
        where G: IntoNeighborsDirected + Visitable<NodeId=N, Map=VM>,
    {
        // Take an unvisited element and find which of its neighbors are next
        while let Some(nix) = self.tovisit.pop() {
            if self.ordered.is_visited(&nix) {
                continue;
            }
            self.ordered.visit(nix);
            for neigh in g.neighbors(nix) {
                // Look at each neighbor, and those that only have incoming edges
                // from the already ordered list, they are the next to visit.
                if Reversed(g).neighbors(neigh).all(|b| self.ordered.is_visited(&b)) {
                    self.tovisit.push(neigh);
                }
            }
            return Some(nix);
        }
        None
    }
}


/// A walker is a traversal state, but where part of the traversal
/// information is supplied manually to each next call.
///
/// This for example allows graph traversals that don't hold a borrow of the
/// graph they are traversing.
pub trait Walker<Context> {
    type Item;
    /// Advance to the next item
    fn walk_next(&mut self, context: Context) -> Option<Self::Item>;

    /// Create an iterator out of the walker and given `context`.
    fn iter(self, context: Context) -> WalkerIter<Self, Context>
        where Self: Sized,
              Context: Clone,
    {
        WalkerIter {
            walker: self,
            context: context,
        }
    }
}

/// A walker and its context wrapped into an iterator.
#[derive(Clone, Debug)]
pub struct WalkerIter<W, C> {
    walker: W,
    context: C,
}

impl<W, C> WalkerIter<W, C>
    where W: Walker<C>,
          C: Clone,
{
    pub fn context(&self) -> C {
        self.context.clone()
    }

    pub fn inner_ref(&self) -> &W {
        &self.walker
    }

    pub fn inner_mut(&mut self) -> &mut W {
        &mut self.walker
    }
}

impl<W, C> Iterator for WalkerIter<W, C>
    where W: Walker<C>,
          C: Clone,
{
    type Item = W::Item;
    fn next(&mut self) -> Option<Self::Item> {
        self.walker.walk_next(self.context.clone())
    }
}

impl<G> Walker<G> for Dfs<G::NodeId, G::Map>
    where G: IntoNeighbors + Visitable
{
    type Item = G::NodeId;
    fn walk_next(&mut self, context: G) -> Option<Self::Item> {
        self.next(context)
    }
}

impl<G> Walker<G> for DfsPostOrder<G::NodeId, G::Map>
    where G: IntoNeighbors + Visitable
{
    type Item = G::NodeId;
    fn walk_next(&mut self, context: G) -> Option<Self::Item> {
        self.next(context)
    }
}

impl<G> Walker<G> for Bfs<G::NodeId, G::Map>
    where G: IntoNeighbors + Visitable
{
    type Item = G::NodeId;
    fn walk_next(&mut self, context: G) -> Option<Self::Item> {
        self.next(context)
    }
}

impl<G> Walker<G> for Topo<G::NodeId, G::Map>
    where G: IntoNeighborsDirected + Visitable,
{
    type Item = G::NodeId;
    fn walk_next(&mut self, context: G) -> Option<Self::Item> {
        self.next(context)
    }
}