squidpony.squidai.graph

Class Algorithms<V>

java.lang.Object

squidpony.squidai.graph.Algorithms<V>

Type Parameters:

V - the vertex type; often Coord

Direct Known Subclasses:

DirectedGraphAlgorithms, UndirectedGraphAlgorithms

public class Algorithms<V>
extends java.lang.Object

Most of the algorithms that operate on a Graph are defined here, with some specific cases in subclasses. The most-frequently-used algorithm here is probably findShortestPath(Object, Object, ArrayList, Heuristic), or some overload of it; this is a standard A-Star algorithm backed by a priority queue that is very fast. Somewhat surprisingly, it doesn't need indices like gdx-ai's IndexedAStarPathFinder needs, and this makes the code easier to use. There's a good amount of other useful algorithms here, like detectCycle() and various non-A-Star search methods, like breadthFirstSearch(Object, int, int) and depthFirstSearch(Object, int, int).
This class is not meant to be extended from outside of this package, so it uses a package-private implementation.

Method Summary

Modifier and Type	Method and Description
Graph<V>	breadthFirstSearch(V v) Perform a breadth first search starting from the specified vertex.
Graph<V>	breadthFirstSearch(V v, int maxVertices, int maxDepth) Perform a breadth first search starting from the specified vertex.
Graph<V>	depthFirstSearch(V v) Perform a depth first search starting from the specified vertex.
Graph<V>	depthFirstSearch(V v, int maxVertices, int maxDepth) Perform a depth first search starting from the specified vertex.
boolean	detectCycle() Checks whether there are any cycles in the graph using depth first searches.
double	findMinimumDistance(V start, V target) Find the length of the shortest path between the start and target vertices, using Dijkstra's algorithm implemented with a priority queue.
java.util.ArrayList<V>	findShortestPath(V start, V target) Find the shortest path between the start and target vertices, using Dijkstra's algorithm implemented with a priority queue.
boolean	findShortestPath(V start, V target, java.util.ArrayList<V> path, Heuristic<V> heuristic) Find the shortest path between the start and target vertices, using the A* search algorithm with the provided heuristic, and implemented with a priority queue.
java.util.ArrayList<V>	findShortestPath(V start, V target, Heuristic<V> heuristic) Find the shortest path between the start and target vertices, using the A* search algorithm with the provided heuristic, and implemented with a priority queue.
int	lastRunID() Gets the identifier for the last run of an algorithm; this should mostly be usable internally, but may be useful when different runs have affected a graph and a Node.lastRunID may need to be checked against this.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

findShortestPath

public java.util.ArrayList<V> findShortestPath(V start,
                                               V target)

Find the shortest path between the start and target vertices, using Dijkstra's algorithm implemented with a priority queue.

Parameters:

start - the starting vertex

target - the target vertex

Returns:

a list of vertices from start to target containing the ordered vertices of a shortest path, including both the start and target vertices

findShortestPath

public java.util.ArrayList<V> findShortestPath(V start,
                                               V target,
                                               Heuristic<V> heuristic)

Find the shortest path between the start and target vertices, using the A* search algorithm with the provided heuristic, and implemented with a priority queue.

Parameters:

start - the starting vertex

target - the target vertex

Returns:

a list of vertices from start to target containing the ordered vertices of a shortest path, including both the start and target vertices

findShortestPath

public boolean findShortestPath(V start,
                                V target,
                                java.util.ArrayList<V> path,
                                Heuristic<V> heuristic)

Find the shortest path between the start and target vertices, using the A* search algorithm with the provided heuristic, and implemented with a priority queue. Fills path with a list of vertices from start to target containing the ordered vertices of a shortest path, including both the start and target vertices.

Parameters:

start - the starting vertex

target - the target vertex

path - the list of vertices to which the path vertices should be added

Returns:

true if a path was found, or false if no path could be found

findMinimumDistance

public double findMinimumDistance(V start,
                                  V target)

Find the length of the shortest path between the start and target vertices, using Dijkstra's algorithm implemented with a priority queue.

Parameters:

start - the starting vertex

target - the target vertex

Returns:

the sum of the weights in a shortest path from the starting vertex to the target vertex

breadthFirstSearch

public Graph<V> breadthFirstSearch(V v,
                                   int maxVertices,
                                   int maxDepth)

Perform a breadth first search starting from the specified vertex.

Parameters:

v - the vertex at which to start the search

maxVertices - the maximum number of vertices to process before terminating the search

maxDepth - the maximum edge distance (the number of edges in a shortest path between vertices) a vertex should have to be considered for processing. If a vertex has a distance larger than the maxDepth, it will not be added to the returned graph

Returns:

a Graph object containing all the processed vertices, and the edges from which each vertex was encountered. The vertices and edges in the returned graph will be in the order they were encountered in the search, and this will be reflected in the iteration order of the collections returned by Graph.getVertices() and Graph.getEdges().

breadthFirstSearch

public Graph<V> breadthFirstSearch(V v)

Perform a breadth first search starting from the specified vertex.

Parameters:

v - the vertex at which to start the search

Returns:

a Graph object containing all the processed vertices (all the vertices in this graph), and the edges from which each vertex was encountered. The vertices and edges in the returned graph will be in the order they were encountered in the search, and this will be reflected in the iteration order of the collections returned by Graph.getVertices() and Graph.getEdges().

depthFirstSearch

public Graph<V> depthFirstSearch(V v,
                                 int maxVertices,
                                 int maxDepth)

Perform a depth first search starting from the specified vertex.

Parameters:

v - the vertex at which to start the search

maxVertices - the maximum number of vertices to process before terminating the search

maxDepth - the maximum edge distance (the number of edges in a shortest path between vertices) a vertex should have to be considered for processing. If a vertex has a distance larger than the maxDepth, it will not be added to the returned graph

Returns:

a Graph object containing all the processed vertices, and the edges from which each vertex was encountered. The vertices and edges in the returned graph will be in the order they were encountered in the search, and this will be reflected in the iteration order of the collections returned by Graph.getVertices() and Graph.getEdges().

depthFirstSearch

public Graph<V> depthFirstSearch(V v)

Perform a depth first search starting from the specified vertex.

Parameters:

v - the vertex at which to start the search

Returns:

a Graph object containing all the processed vertices (all the vertices in this graph), and the edges from which each vertex was encountered. The vertices and edges in the returned graph will be in the order they were encountered in the search, and this will be reflected in the iteration order of the collections returned by Graph.getVertices() and Graph.getEdges().

detectCycle

public boolean detectCycle()

Checks whether there are any cycles in the graph using depth first searches.

Returns:

true if the graph contains a cycle, false otherwise

lastRunID

public int lastRunID()

Gets the identifier for the last run of an algorithm; this should mostly be usable internally, but may be useful when different runs have affected a graph and a Node.lastRunID may need to be checked against this.

Returns:

an identifier for which algorithm ran last, as a probably-unique int