| 1 | /* |
| 2 | * $Id: Traversers.java 594 2010-11-19 20:41:04Z PSpeed $ |
| 3 | * |
| 4 | * The Filament BSD license. |
| 5 | * |
| 6 | * Copyright (c) 2009-2010, the original author or authors |
| 7 | * |
| 8 | * Redistribution and use in source and binary forms, with or without |
| 9 | * modification, are permitted provided that the following conditions |
| 10 | * are met: |
| 11 | * |
| 12 | * 1) Redistributions of source code must retain the above copyright notice, |
| 13 | * this list of conditions and the following disclaimer. |
| 14 | * 2) Redistributions in binary form must reproduce the above copyright |
| 15 | * notice, this list of conditions and the following disclaimer in the |
| 16 | * documentation and/or other materials provided with the distribution. |
| 17 | * 3) Neither the names "Filament", "fgraph.org", "filamentgraph.org", nor the |
| 18 | * names of its contributors may be used to endorse or promote products |
| 19 | * derived from this software without specific prior written permission. |
| 20 | * |
| 21 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
| 22 | * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| 23 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| 24 | * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE |
| 25 | * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| 26 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| 27 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| 28 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| 29 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| 30 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| 31 | * POSSIBILITY OF SUCH DAMAGE. |
| 32 | */ |
| 33 | |
| 34 | package org.fgraph.steps; |
| 35 | |
| 36 | import java.util.*; |
| 37 | |
| 38 | import com.google.common.base.Function; |
| 39 | import com.google.common.base.Predicate; |
| 40 | import com.google.common.collect.Iterables; |
| 41 | import com.google.common.collect.Iterators; |
| 42 | |
| 43 | |
| 44 | /** |
| 45 | * Factory methods for creating traverser Iterables. |
| 46 | * |
| 47 | * @version $Revision: 594 $ |
| 48 | * @author Paul Speed |
| 49 | */ |
| 50 | public class Traversers |
| 51 | { |
| 52 | /** |
| 53 | * Creates an Iterable that performs a pre-order depth-first |
| 54 | * traversal starting at a specified node and using the specified |
| 55 | * adjacency function for traversal. |
| 56 | * |
| 57 | * <p>If an optional visitMarker function is provided then the |
| 58 | * traversal is acyclic based on the 'marker' returned from that |
| 59 | * function. For example, a Functions.identity() visit marker |
| 60 | * will make sure a node is only visited once based on its own |
| 61 | * .equals() implementation. A null indicates that no cycle |
| 62 | * detection should be performed.</p> |
| 63 | */ |
| 64 | public static <T> Iterable<T> preOrder( T start, Function<T,? extends Iterable<T>> fstep, |
| 65 | Function<? super T,? extends Object> visitMarker ) |
| 66 | { |
| 67 | Iterable<DepthFirstStep<T>> pre = preOrderSteps( start, fstep, visitMarker ); |
| 68 | return Iterables.transform( pre, StepFunctions.<T>unwrapStep() ); |
| 69 | } |
| 70 | |
| 71 | /** |
| 72 | * Creates a function that performs a pre-order depth-first |
| 73 | * traversal starting at a specified node and using the specified |
| 74 | * adjacency function for traversal, also providing additional |
| 75 | * control over and information about the ongoing traversal. |
| 76 | * |
| 77 | * <p>This is similar to the non-step based version except that |
| 78 | * the traversed values are returned wrapped in DepthFirstStep |
| 79 | * objects that provide additional information about the state |
| 80 | * of the traversal such as depth. These steps also allow themselves |
| 81 | * to be 'pruned', resulting in any potential descendants being ignored |
| 82 | * during the subsequent traverses.</p> |
| 83 | * |
| 84 | * <p>If an optional visitMarker function is provided then the |
| 85 | * traversal is acyclic based on the 'marker' returned from that |
| 86 | * function. For example, a Functions.identity() visit marker |
| 87 | * will make sure a node is only visited once based on its own |
| 88 | * .equals() implementation. A null indicates that no cycle |
| 89 | * detection should be performed.</p> |
| 90 | */ |
| 91 | public static <T> Iterable<DepthFirstStep<T>> preOrderSteps( T start, |
| 92 | Function<T,? extends Iterable<T>> fstep, |
| 93 | Function<? super T,? extends Object> visitMarker ) |
| 94 | { |
| 95 | Iterable<DepthFirstStep<T>> depth = depthFirstSteps(start, fstep, visitMarker); |
| 96 | return Iterables.filter( depth, StepPredicates.<T>descending() ); |
| 97 | } |
| 98 | |
| 99 | /** |
| 100 | * Creates a function that performs a post-order depth-first |
| 101 | * traversal starting at a specified node and using the specified |
| 102 | * adjacency function for traversal. |
| 103 | * |
| 104 | * <p>If an optional visitMarker function is provided then the |
| 105 | * traversal is acyclic based on the 'marker' returned from that |
| 106 | * function. For example, a Functions.identity() visit marker |
| 107 | * will make sure a node is only visited once based on its own |
| 108 | * .equals() implementation. A null indicates that no cycle |
| 109 | * detection should be performed.</p> |
| 110 | */ |
| 111 | public static <T> Iterable<T> postOrder( T start, Function<T,? extends Iterable<T>> fstep, |
| 112 | Function<? super T,? extends Object> visitMarker ) |
| 113 | { |
| 114 | Iterable<DepthFirstStep<T>> post = postOrderSteps( start, fstep, visitMarker ); |
| 115 | return Iterables.transform( post, StepFunctions.<T>unwrapStep() ); |
| 116 | } |
| 117 | |
| 118 | /** |
| 119 | * Creates a function that performs a post-order depth-first |
| 120 | * traversal starting at a specified node and using the specified |
| 121 | * adjacency function for traversal, also providing additional |
| 122 | * control over and information about the ongoing traversal. |
| 123 | * |
| 124 | * <p>This is similar to the non-step based version except that |
| 125 | * the traversed values are returned wrapped in DepthFirstStep |
| 126 | * objects that provide additional information about the state |
| 127 | * of the traversal such as depth. These steps also allow themselves |
| 128 | * to be 'pruned', resulting in any potential descendants being ignored |
| 129 | * during the subsequent traverses.</p> |
| 130 | * |
| 131 | * <p>If an optional visitMarker function is provided then the |
| 132 | * traversal is acyclic based on the 'marker' returned from that |
| 133 | * function. For example, a Functions.identity() visit marker |
| 134 | * will make sure a node is only visited once based on its own |
| 135 | * .equals() implementation. A null indicates that no cycle |
| 136 | * detection should be performed.</p> |
| 137 | */ |
| 138 | public static <T> Iterable<DepthFirstStep<T>> postOrderSteps( T start, |
| 139 | Function<T,? extends Iterable<T>> fstep, |
| 140 | Function<? super T,? extends Object> visitMarker ) |
| 141 | { |
| 142 | Iterable<DepthFirstStep<T>> depth = depthFirstSteps( start, fstep, visitMarker ); |
| 143 | return Iterables.filter( depth, StepPredicates.<T>ascending() ); |
| 144 | } |
| 145 | |
| 146 | /** |
| 147 | * Creates a function that performs a full depth-first |
| 148 | * traversal (both pre- and post-) starting at a specified node |
| 149 | * and using the specified adjacency function for traversal. |
| 150 | * Every 'node' will therefore be visited twice, once descending |
| 151 | * and once ascending. Use the step-based depthFirstSteps() |
| 152 | * method to distinguish descending from ascending. |
| 153 | * |
| 154 | * <p>If an optional visitMarker function is provided then the |
| 155 | * traversal is acyclic based on the 'marker' returned from that |
| 156 | * function. For example, a Functions.identity() visit marker |
| 157 | * will make sure a node is only visited once based on its own |
| 158 | * .equals() implementation. A null indicates that no cycle |
| 159 | * detection should be performed.</p> |
| 160 | */ |
| 161 | public static <T> Iterable<T> depthFirst( T start, Function<T,? extends Iterable<T>> fstep, |
| 162 | Function<? super T,? extends Object> visitMarker ) |
| 163 | { |
| 164 | Iterable<DepthFirstStep<T>> depth = depthFirstSteps( start, fstep, visitMarker ); |
| 165 | return Iterables.transform( depth, StepFunctions.<T>unwrapStep() ); |
| 166 | } |
| 167 | |
| 168 | /** |
| 169 | * Creates a function that performs a full depth-first |
| 170 | * traversal (both pre- and post-) starting at a specified node |
| 171 | * and using the specified adjacency function for traversal, |
| 172 | * also providing additional control over and information about |
| 173 | * the ongoing traversal. |
| 174 | * |
| 175 | * <p>This is similar to the non-step based version except that |
| 176 | * the traversed values are returned wrapped in DepthFirstStep |
| 177 | * objects that provide additional information about the state |
| 178 | * of the traversal such as depth, descending/ascending, etc. |
| 179 | * These steps also allow themselves to be 'pruned', resulting |
| 180 | * in any potential descendants being ignored during the subsequent |
| 181 | * traverses.</p> |
| 182 | * |
| 183 | * <p>If an optional visitMarker function is provided then the |
| 184 | * traversal is acyclic based on the 'marker' returned from that |
| 185 | * function. For example, a Functions.identity() visit marker |
| 186 | * will make sure a node is only visited once based on its own |
| 187 | * .equals() implementation. A null indicates that no cycle |
| 188 | * detection should be performed.</p> |
| 189 | */ |
| 190 | public static <T> Iterable<DepthFirstStep<T>> depthFirstSteps( T start, |
| 191 | Function<T,? extends Iterable<T>> fstep, |
| 192 | Function<? super T,? extends Object> visitMarker ) |
| 193 | { |
| 194 | return new DepthFirstIterable<T>( start, fstep, visitMarker ); |
| 195 | } |
| 196 | |
| 197 | /** |
| 198 | * Creates a function that performs a breadth-first |
| 199 | * traversal starting at a specified node and using the specified |
| 200 | * adjacency function for traversal. |
| 201 | * |
| 202 | * <p>If an optional visitMarker function is provided then the |
| 203 | * traversal is acyclic based on the 'marker' returned from that |
| 204 | * function. For example, a Functions.identity() visit marker |
| 205 | * will make sure a node is only visited once based on its own |
| 206 | * .equals() implementation. A null indicates that no cycle |
| 207 | * detection should be performed.</p> |
| 208 | */ |
| 209 | public static <T> Iterable<T> breadthFirst( T start, Function<T,? extends Iterable<T>> fstep, |
| 210 | Function<? super T,? extends Object> visitMarker ) |
| 211 | { |
| 212 | Iterable<PrunableStep<T>> breadth = breadthFirstSteps(start, fstep, visitMarker); |
| 213 | return Iterables.transform( breadth, StepFunctions.<T>unwrapStep() ); |
| 214 | } |
| 215 | |
| 216 | /** |
| 217 | * Creates a function that performs a breadth-first |
| 218 | * traversal starting at a specified node and using the specified |
| 219 | * adjacency function for traversal, also providing additional |
| 220 | * control over and information about the ongoing traversal. |
| 221 | * |
| 222 | * <p>This is similar to the non-step based version except that |
| 223 | * the traversed values are returned wrapped in PrunableStep |
| 224 | * objects that provide additional information about the state |
| 225 | * of the traversal such as depth. These steps also allow themselves |
| 226 | * to be 'pruned', resulting in any potential descendants being ignored |
| 227 | * during the subsequent traverses.</p> |
| 228 | * |
| 229 | * <p>If an optional visitMarker function is provided then the |
| 230 | * traversal is acyclic based on the 'marker' returned from that |
| 231 | * function. For example, a Functions.identity() visit marker |
| 232 | * will make sure a node is only visited once based on its own |
| 233 | * .equals() implementation. A null indicates that no cycle |
| 234 | * detection should be performed.</p> |
| 235 | */ |
| 236 | public static <T> Iterable<PrunableStep<T>> breadthFirstSteps( T start, |
| 237 | Function<T,? extends Iterable<T>> fstep, |
| 238 | Function<? super T,? extends Object> visitMarker ) |
| 239 | { |
| 240 | return new BreadthFirstIterable<T>( start, fstep, visitMarker ); |
| 241 | } |
| 242 | |
| 243 | /** |
| 244 | * Creates a function that performs a priority-ordered |
| 245 | * traversal starting at a specified node and using the specified |
| 246 | * adjacency function for traversal. |
| 247 | * |
| 248 | * <p>The priority comparator is used to select the next step/path |
| 249 | * from the current pending set of descendants. For example, a |
| 250 | * comparator could be based to select the smallest/shortest route |
| 251 | * based on the sum of the accumulated weights/distances up to that step.</p> |
| 252 | * |
| 253 | * <p>If an optional visitMarker function is provided then the |
| 254 | * traversal is acyclic based on the 'marker' returned from that |
| 255 | * function. For example, a Functions.identity() visit marker |
| 256 | * will make sure a node is only visited once based on its own |
| 257 | * .equals() implementation. A null indicates that no cycle |
| 258 | * detection should be performed.</p> |
| 259 | */ |
| 260 | public static <T> Iterable<T> priority( T start, Function<T,? extends Iterable<T>> fstep, |
| 261 | Comparator<? super T> priority, |
| 262 | Function<? super T,? extends Object> visitMarker ) |
| 263 | { |
| 264 | Iterable<PrunableStep<T>> pri = prioritySteps( start, fstep, priority, visitMarker ); |
| 265 | return Iterables.transform( pri, StepFunctions.<T>unwrapStep() ); |
| 266 | } |
| 267 | |
| 268 | /** |
| 269 | * Creates a function that performs a priority-ordered |
| 270 | * traversal starting at a specified node and using the specified |
| 271 | * adjacency function for traversal, also providing additional |
| 272 | * control over and information about the ongoing traversal. |
| 273 | * |
| 274 | * <p>The priority comparator is used to select the next step/path |
| 275 | * from the current pending set of descendants. For example, a |
| 276 | * comparator could be based to select the smallest/shortest route |
| 277 | * based on the sum of the accumulated weights/distances up to that step.</p> |
| 278 | * |
| 279 | * <p>This is similar to the non-step based version except that |
| 280 | * the traversed values are returned wrapped in PrunableStep |
| 281 | * objects that provide additional information about the state |
| 282 | * of the traversal such as depth. These steps also allow themselves |
| 283 | * to be 'pruned', resulting in any potential descendants being ignored |
| 284 | * during the subsequent traverses. Note: for traversals that branch |
| 285 | * quickly, pruning a step may be a non-trivial amount of work since |
| 286 | * it must exhaustively search the current sorted pending steps to |
| 287 | * remove any queued descendants.</p> |
| 288 | * |
| 289 | * <p>If an optional visitMarker function is provided then the |
| 290 | * traversal is acyclic based on the 'marker' returned from that |
| 291 | * function. For example, a Functions.identity() visit marker |
| 292 | * will make sure a node is only visited once based on its own |
| 293 | * .equals() implementation. A null indicates that no cycle |
| 294 | * detection should be performed.</p> |
| 295 | */ |
| 296 | public static <T> Iterable<PrunableStep<T>> prioritySteps( T start, |
| 297 | Function<T,? extends Iterable<T>> fstep, |
| 298 | Comparator<? super T> priority, |
| 299 | Function<? super T,? extends Object> visitMarker ) |
| 300 | { |
| 301 | return new PriorityTraverseIterable<T>( start, fstep, priority, visitMarker ); |
| 302 | } |
| 303 | |
| 304 | /** |
| 305 | * Method used internally to wrap an adjacency function in a |
| 306 | * stateful function that tracks visits using the specified |
| 307 | * visit marker function. |
| 308 | */ |
| 309 | protected static <T> StepFunction<T,T> distinct( Function<T,? extends Iterable<T>> fstep, |
| 310 | Function<? super T,? extends Object> visitMarker ) |
| 311 | { |
| 312 | return new DistinctStepFunction<T>( visitMarker, fstep ); |
| 313 | } |
| 314 | |
| 315 | /** |
| 316 | * Internal implementation of Iterable that delegates |
| 317 | * to the abstract stepIterator() method. |
| 318 | */ |
| 319 | protected static abstract class StepIterable<S,T> implements Iterable<T> |
| 320 | { |
| 321 | private S start; |
| 322 | |
| 323 | /** |
| 324 | * Constructs an iterable that simply delegates |
| 325 | * to the stepIterator() method. |
| 326 | */ |
| 327 | public StepIterable( S start ) |
| 328 | { |
| 329 | this.start = start; |
| 330 | } |
| 331 | |
| 332 | protected S getStart() |
| 333 | { |
| 334 | return start; |
| 335 | } |
| 336 | |
| 337 | protected abstract Iterator<T> stepIterator( S start ); |
| 338 | |
| 339 | /** |
| 340 | * {@inheritDoc} |
| 341 | */ |
| 342 | public Iterator<T> iterator() |
| 343 | { |
| 344 | return stepIterator(start); |
| 345 | } |
| 346 | } |
| 347 | |
| 348 | private static class DepthFirstIterable<T> extends StepIterable<T,DepthFirstStep<T>> |
| 349 | { |
| 350 | private Function<T,? extends Iterable<T>> fstep; |
| 351 | private Function<? super T,? extends Object> visitMarker; |
| 352 | |
| 353 | public DepthFirstIterable( T start, Function<T,? extends Iterable<T>> fstep, |
| 354 | Function<? super T,? extends Object> visitMarker ) |
| 355 | { |
| 356 | super( start ); |
| 357 | this.fstep = fstep; |
| 358 | this.visitMarker = visitMarker; |
| 359 | } |
| 360 | |
| 361 | protected Iterator<DepthFirstStep<T>> stepIterator( T start ) |
| 362 | { |
| 363 | if( visitMarker != null ) |
| 364 | return new DepthFirstTraverser<T>( start, distinct( fstep, visitMarker ) ); |
| 365 | return new DepthFirstTraverser<T>( start, fstep ); |
| 366 | } |
| 367 | |
| 368 | public String toString() |
| 369 | { |
| 370 | return "DepthFirstIterable[start=" + getStart() |
| 371 | + ", delegate=" + fstep |
| 372 | + ", visitMarker=" + visitMarker + "]"; |
| 373 | } |
| 374 | } |
| 375 | |
| 376 | /** |
| 377 | * Function implementation that creates breadth first iterators on demand. |
| 378 | */ |
| 379 | private static class BreadthFirstIterable<T> extends StepIterable<T,PrunableStep<T>> |
| 380 | { |
| 381 | private Function<T,? extends Iterable<T>> fstep; |
| 382 | private Function<? super T,? extends Object> visitMarker; |
| 383 | |
| 384 | public BreadthFirstIterable( T start, Function<T,? extends Iterable<T>> fstep, |
| 385 | Function<? super T,? extends Object> visitMarker ) |
| 386 | { |
| 387 | super( start ); |
| 388 | this.fstep = fstep; |
| 389 | this.visitMarker = visitMarker; |
| 390 | } |
| 391 | |
| 392 | protected Iterator<PrunableStep<T>> stepIterator( T start ) |
| 393 | { |
| 394 | if( visitMarker != null ) |
| 395 | return new BreadthFirstTraverser<T>( start, distinct( fstep, visitMarker ) ); |
| 396 | return new BreadthFirstTraverser<T>( start, fstep ); |
| 397 | } |
| 398 | |
| 399 | public String toString() |
| 400 | { |
| 401 | return "BreadthFirstIterable[start=" + getStart() |
| 402 | + ", delegate=" + fstep |
| 403 | + ", visitMarker=" + visitMarker + "]"; |
| 404 | } |
| 405 | } |
| 406 | |
| 407 | /** |
| 408 | * Function implementation that creates priority first iterators on demand. |
| 409 | */ |
| 410 | private static class PriorityTraverseIterable<T> extends StepIterable<T,PrunableStep<T>> |
| 411 | { |
| 412 | private Function<T,? extends Iterable<T>> fstep; |
| 413 | private Comparator<? super T> priority; |
| 414 | private Function<? super T,? extends Object> visitMarker; |
| 415 | |
| 416 | public PriorityTraverseIterable( T start, Function<T,? extends Iterable<T>> fstep, |
| 417 | Comparator<? super T> priority, |
| 418 | Function<? super T,? extends Object> visitMarker ) |
| 419 | { |
| 420 | super( start ); |
| 421 | this.fstep = fstep; |
| 422 | this.priority = priority; |
| 423 | this.visitMarker = visitMarker; |
| 424 | } |
| 425 | |
| 426 | protected Iterator<PrunableStep<T>> stepIterator( T start ) |
| 427 | { |
| 428 | if( visitMarker != null ) |
| 429 | return new PriorityTraverser<T>( start, distinct( fstep, visitMarker ), priority ); |
| 430 | return new PriorityTraverser<T>( start, fstep, priority ); |
| 431 | } |
| 432 | |
| 433 | public String toString() |
| 434 | { |
| 435 | return "PriorityTraverseIterable[start=" + getStart() |
| 436 | + ", delegate=" + fstep |
| 437 | + ", priority=" + priority |
| 438 | + ", visitMarker=" + visitMarker + "]"; |
| 439 | } |
| 440 | } |
| 441 | |
| 442 | /** |
| 443 | * Stateful predicate returns true for newly encountered |
| 444 | * items and adds them to an internal set. A marker function |
| 445 | * is used to translate raw values into visit-tracking |
| 446 | * markers. |
| 447 | */ |
| 448 | private static class IsNewObject<T> implements Predicate<T> |
| 449 | { |
| 450 | private Set<Object> visited = new HashSet<Object>(); |
| 451 | private Function<? super T,? extends Object> visitMarker; |
| 452 | |
| 453 | public IsNewObject( Function<? super T,? extends Object> visitMarker ) |
| 454 | { |
| 455 | this.visitMarker = visitMarker; |
| 456 | } |
| 457 | |
| 458 | public boolean apply( T value ) |
| 459 | { |
| 460 | Object marker = visitMarker.apply(value); |
| 461 | return visited.add(marker); |
| 462 | } |
| 463 | } |
| 464 | |
| 465 | /** |
| 466 | * Stateful function for returning only distinct |
| 467 | * values. |
| 468 | */ |
| 469 | private static class DistinctStepFunction<T> implements StepFunction<T,T> |
| 470 | { |
| 471 | private IsNewObject<T> newObject; |
| 472 | private Function<T, ? extends Iterable<T>> delegate; |
| 473 | |
| 474 | public DistinctStepFunction( Function<? super T,? extends Object> visitMarker, |
| 475 | Function<T, ? extends Iterable<T>> delegate ) |
| 476 | { |
| 477 | this.newObject = new IsNewObject<T>(visitMarker); |
| 478 | this.delegate = delegate; |
| 479 | } |
| 480 | |
| 481 | public Iterable<T> apply( T value ) |
| 482 | { |
| 483 | newObject.apply( value ); |
| 484 | return Iterables.filter( delegate.apply( value ), newObject ); |
| 485 | } |
| 486 | } |
| 487 | |
| 488 | /** |
| 489 | * PrunableStep implementation that has reference back to its creating |
| 490 | * Traverser for pruning. Internally this keeps track of some data |
| 491 | * structures useful to the traverser implementations. |
| 492 | */ |
| 493 | private static class TraversalStep<T> implements PrunableStep<T> |
| 494 | { |
| 495 | private Traverser traverser; |
| 496 | private Step parent; |
| 497 | private int depth; |
| 498 | private T node; |
| 499 | |
| 500 | public TraversalStep( Traverser traverser, Step parent, T node ) |
| 501 | { |
| 502 | this.traverser = traverser; |
| 503 | this.parent = parent; |
| 504 | this.node = node; |
| 505 | if( parent == null ) |
| 506 | depth = 0; |
| 507 | else |
| 508 | depth = parent.getDepth() + 1; |
| 509 | } |
| 510 | |
| 511 | public T getValue() |
| 512 | { |
| 513 | return node; |
| 514 | } |
| 515 | |
| 516 | public int getDepth() |
| 517 | { |
| 518 | return depth; |
| 519 | } |
| 520 | |
| 521 | public Step getParent() |
| 522 | { |
| 523 | return parent; |
| 524 | } |
| 525 | |
| 526 | public void prune() |
| 527 | { |
| 528 | traverser.prune(this); |
| 529 | } |
| 530 | |
| 531 | public String toString() |
| 532 | { |
| 533 | return getClass().getSimpleName() + "[" + node + ", " + depth + "]"; |
| 534 | } |
| 535 | } |
| 536 | |
| 537 | /** |
| 538 | * Depth first specific step implementation. |
| 539 | */ |
| 540 | private static class DfsStep<T> extends TraversalStep<T> |
| 541 | implements DepthFirstStep<T> |
| 542 | { |
| 543 | private Iterator<T> it; |
| 544 | private int descending = -1; |
| 545 | |
| 546 | public DfsStep( Traverser traverser, DfsStep<T> parent, T node ) |
| 547 | { |
| 548 | super( traverser, parent, node ); |
| 549 | } |
| 550 | |
| 551 | protected Iterator<T> iterator() |
| 552 | { |
| 553 | return it; |
| 554 | } |
| 555 | |
| 556 | protected void setIterator( Iterator<T> it ) |
| 557 | { |
| 558 | this.it = it; |
| 559 | } |
| 560 | |
| 561 | protected int descending() |
| 562 | { |
| 563 | return descending; |
| 564 | } |
| 565 | |
| 566 | protected void setDescending( int descending ) |
| 567 | { |
| 568 | this.descending = descending; |
| 569 | } |
| 570 | |
| 571 | public boolean isDescending() |
| 572 | { |
| 573 | return descending <= 0; |
| 574 | } |
| 575 | |
| 576 | public String toString() |
| 577 | { |
| 578 | return getClass().getSimpleName() + "[" + getValue() + ", " + getDepth() |
| 579 | + ", " + isDescending() + "]"; |
| 580 | } |
| 581 | } |
| 582 | |
| 583 | /** |
| 584 | * Base class for the various traverser iterator implementations. |
| 585 | * Exposes an abstract prune() that the specific implementations |
| 586 | * must implement. |
| 587 | */ |
| 588 | protected abstract static class Traverser<T> implements Iterator<T> |
| 589 | { |
| 590 | /** |
| 591 | * Implemented by the specific traversers to provide |
| 592 | * implementation specific pruning. |
| 593 | */ |
| 594 | protected abstract void prune( PrunableStep step ); |
| 595 | } |
| 596 | |
| 597 | /** |
| 598 | * The depth-first stateful traversal implementation. |
| 599 | */ |
| 600 | private static class DepthFirstTraverser<T> extends Traverser<DepthFirstStep<T>> |
| 601 | { |
| 602 | private T start; |
| 603 | private Function<T,? extends Iterable<T>> fstep; |
| 604 | private LinkedList<DfsStep<T>> stack = new LinkedList<DfsStep<T>>(); |
| 605 | |
| 606 | public DepthFirstTraverser( T start, Function<T,? extends Iterable<T>> fstep ) |
| 607 | { |
| 608 | this.start = start; |
| 609 | this.fstep = fstep; |
| 610 | stack.addFirst( new DfsStep<T>(this, null, start) ); |
| 611 | } |
| 612 | |
| 613 | protected void prune( PrunableStep step ) |
| 614 | { |
| 615 | // For now, we'll only support pruning the current level... |
| 616 | // though there's not a strong reason not to support multi-level |
| 617 | // pruning it just seems a little dangerous. |
| 618 | if( stack.getFirst() != step ) |
| 619 | throw new IllegalStateException( "Pruned step is not current." ); |
| 620 | |
| 621 | // Otherwise, just remove it |
| 622 | stack.removeFirst(); |
| 623 | } |
| 624 | |
| 625 | public boolean hasNext() |
| 626 | { |
| 627 | // Since we remove the last item when we're done |
| 628 | // then this is enough of a check... since |
| 629 | // even an item with no children is returned on |
| 630 | // exit (and then removed). |
| 631 | return !stack.isEmpty(); |
| 632 | } |
| 633 | |
| 634 | public DepthFirstStep<T> next() |
| 635 | { |
| 636 | while( true ) |
| 637 | { |
| 638 | // See what the state of the top item is |
| 639 | DfsStep<T> top = stack.getFirst(); |
| 640 | |
| 641 | if( top.iterator() == null && top.descending() < 0 ) |
| 642 | { |
| 643 | // Mark it as leveling off and we'll create |
| 644 | // the iterator the next time through |
| 645 | top.setDescending(0); |
| 646 | return top; // descending |
| 647 | } |
| 648 | else if( top.iterator() == null ) |
| 649 | { |
| 650 | top.setIterator( fstep.apply( top.getValue() ).iterator() ); |
| 651 | } |
| 652 | |
| 653 | if( !top.it.hasNext() ) |
| 654 | { |
| 655 | // Then we're done with this level |
| 656 | stack.removeFirst(); |
| 657 | top.setDescending(1); |
| 658 | return top; // ascending |
| 659 | } |
| 660 | |
| 661 | // Otherwise, just return the next element in |
| 662 | // the steps iterator |
| 663 | T result = top.iterator().next(); |
| 664 | stack.addFirst( new DfsStep<T>(this, top, result) ); |
| 665 | } |
| 666 | } |
| 667 | |
| 668 | public void remove() |
| 669 | { |
| 670 | throw new UnsupportedOperationException(); |
| 671 | } |
| 672 | } |
| 673 | |
| 674 | /** |
| 675 | * The breadth-first stateful traversal implementation. |
| 676 | */ |
| 677 | private static class BreadthFirstTraverser<T> extends Traverser<PrunableStep<T>> |
| 678 | { |
| 679 | private T start; |
| 680 | private Function<T,? extends Iterable<T>> fstep; |
| 681 | private LinkedList<TraversalStep<T>> queue = new LinkedList<TraversalStep<T>>(); |
| 682 | private TraversalStep<T> parent; |
| 683 | private Iterator<T> current; |
| 684 | |
| 685 | public BreadthFirstTraverser( T start, Function<T,? extends Iterable<T>> fstep ) |
| 686 | { |
| 687 | this.start = start; |
| 688 | this.fstep = fstep; |
| 689 | parent = null; |
| 690 | current = Iterators.singletonIterator(start); |
| 691 | } |
| 692 | |
| 693 | protected void prune( PrunableStep step ) |
| 694 | { |
| 695 | // In this implementation of breadth-first traveral, |
| 696 | // when the current value has been returned, the |
| 697 | // step is added to the end of the queue and it's |
| 698 | // from there that we should remove it. |
| 699 | if( queue.getLast() != step ) |
| 700 | throw new IllegalStateException( "Pruned step is not current." ); |
| 701 | queue.removeLast(); |
| 702 | } |
| 703 | |
| 704 | public boolean hasNext() |
| 705 | { |
| 706 | if( current.hasNext() ) |
| 707 | return true; |
| 708 | |
| 709 | while( !queue.isEmpty() ) |
| 710 | { |
| 711 | parent = queue.removeFirst(); |
| 712 | current = fstep.apply( parent.node ).iterator(); |
| 713 | if( current.hasNext() ) |
| 714 | return true; |
| 715 | } |
| 716 | |
| 717 | return false; |
| 718 | } |
| 719 | |
| 720 | public PrunableStep<T> next() |
| 721 | { |
| 722 | if( !hasNext() ) |
| 723 | throw new NoSuchElementException(); |
| 724 | |
| 725 | // At this point we are guaranteed to have a current |
| 726 | // iterator with stuff still in it. |
| 727 | T next = current.next(); |
| 728 | TraversalStep<T> result = new TraversalStep<T>(this, parent, next); |
| 729 | queue.addLast( result ); |
| 730 | |
| 731 | return result; |
| 732 | } |
| 733 | |
| 734 | public void remove() |
| 735 | { |
| 736 | throw new UnsupportedOperationException(); |
| 737 | } |
| 738 | } |
| 739 | |
| 740 | /** |
| 741 | * Comparator that can unwrap steps for comparison by a delegate |
| 742 | * comparator. This is used by the PriorityTraverser to priority |
| 743 | * sort the pending steps. |
| 744 | */ |
| 745 | private static class StepComparator<T> implements Comparator<Step<T>> |
| 746 | { |
| 747 | private Comparator<? super T> delegate; |
| 748 | |
| 749 | public StepComparator( Comparator<? super T> delegate ) |
| 750 | { |
| 751 | this.delegate = delegate; |
| 752 | } |
| 753 | |
| 754 | public int compare( Step<T> s1, Step<T> s2 ) |
| 755 | { |
| 756 | return delegate.compare( s1.getValue(), s2.getValue() ); |
| 757 | } |
| 758 | } |
| 759 | |
| 760 | /** |
| 761 | * The priority-ordered stateful traversal implementation. |
| 762 | */ |
| 763 | private static class PriorityTraverser<T> extends Traverser<PrunableStep<T>> |
| 764 | { |
| 765 | private static final int INITIAL_CAPACITY = 11; // the same as PriorityQueue's default |
| 766 | |
| 767 | private T start; |
| 768 | private Function<T,? extends Iterable<T>> fstep; |
| 769 | private Comparator<? super T> priority; |
| 770 | |
| 771 | private PriorityQueue<PrunableStep<T>> pending; |
| 772 | private PrunableStep<T> last; |
| 773 | |
| 774 | public PriorityTraverser( T start, Function<T,? extends Iterable<T>> fstep, |
| 775 | Comparator<? super T> priority ) |
| 776 | { |
| 777 | this.start = start; |
| 778 | this.fstep = fstep; |
| 779 | this.priority = priority; |
| 780 | |
| 781 | this.pending = new PriorityQueue<PrunableStep<T>>( INITIAL_CAPACITY, |
| 782 | new StepComparator<T>(priority) ); |
| 783 | pending.add( new TraversalStep<T>( this, null, start ) ); |
| 784 | } |
| 785 | |
| 786 | protected void addChildren( PrunableStep<T> parent ) |
| 787 | { |
| 788 | for( T child : fstep.apply( parent.getValue() ) ) |
| 789 | { |
| 790 | pending.add( new TraversalStep<T>( this, parent, child ) ); |
| 791 | } |
| 792 | } |
| 793 | |
| 794 | protected void prune( PrunableStep step ) |
| 795 | { |
| 796 | // If the step isn't the last one returned then |
| 797 | // we don't allow it. In this case, it really is |
| 798 | // tricky to implement that. |
| 799 | if( step != last ) |
| 800 | throw new IllegalStateException( "Pruned step is not current." ); |
| 801 | |
| 802 | // Remove any steps that have the specified step |
| 803 | // as parent. There is no cheap way to do this |
| 804 | for( Iterator<PrunableStep<T>> i = pending.iterator(); i.hasNext(); ) |
| 805 | { |
| 806 | PrunableStep s = i.next(); |
| 807 | if( s.getParent() == step ) |
| 808 | i.remove(); |
| 809 | } |
| 810 | } |
| 811 | |
| 812 | public boolean hasNext() |
| 813 | { |
| 814 | return !pending.isEmpty(); |
| 815 | } |
| 816 | |
| 817 | public PrunableStep<T> next() |
| 818 | { |
| 819 | if( !hasNext() ) |
| 820 | throw new NoSuchElementException(); |
| 821 | |
| 822 | // Grab the top of the queue |
| 823 | last = pending.remove(); |
| 824 | |
| 825 | // Fetch any next level steps before returning |
| 826 | addChildren( last ); |
| 827 | |
| 828 | return last; |
| 829 | } |
| 830 | |
| 831 | public void remove() |
| 832 | { |
| 833 | throw new UnsupportedOperationException(); |
| 834 | } |
| 835 | } |
| 836 | } |
| 837 | |