Package 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 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.
Author:
earlygrey

  • Method Summary

    Modifier and Type Method 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.
    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, 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.
    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 Details

    • findShortestPath

      public 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 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, 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