Package edu.princeton.cs.algs4

Class BreadthFirstDirectedPaths

Object

edu.princeton.cs.algs4.BreadthFirstDirectedPaths

public class BreadthFirstDirectedPaths
extends Object

The BreadthDirectedFirstPaths class represents a data type for finding shortest paths (number of edges) from a source vertex s (or set of source vertices) to every other vertex in the digraph.

This implementation uses breadth-first search. The constructor takes Θ(V + E) time in the worst case, where V is the number of vertices and E is the number of edges. Each instance method takes Θ(1) time. It uses Θ(V) extra space (not including the digraph).

For additional documentation, see Section 4.2 of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.

Author:

Robert Sedgewick, Kevin Wayne

Constructor Summary

Constructors

Constructor	Description
BreadthFirstDirectedPaths(Digraph G, int s)	Computes the shortest path from s and every other vertex in graph G.
BreadthFirstDirectedPaths(Digraph G, Iterable<Integer> sources)	Computes the shortest path from any one of the source vertices in sources to every other vertex in graph G.

Method Summary

Modifier and Type	Method	Description
int	distTo(int v)	Returns the number of edges in a shortest path from the source s (or sources) to vertex v?
boolean	hasPathTo(int v)	Is there a directed path from the source s (or sources) to vertex v?
static void	main(String[] args)	Unit tests the BreadthFirstDirectedPaths data type.
Iterable<Integer>	pathTo(int v)	Returns a shortest path from s (or sources) to v, or null if no such path.

Methods inherited from class java.lang.Object

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

Constructor Detail

BreadthFirstDirectedPaths

public BreadthFirstDirectedPaths(Digraph G,
                                 int s)

Computes the shortest path from s and every other vertex in graph G.

Parameters:

G - the digraph

s - the source vertex

Throws:

IllegalArgumentException - unless 0 <= v < V

BreadthFirstDirectedPaths

public BreadthFirstDirectedPaths(Digraph G,
                                 Iterable<Integer> sources)

Computes the shortest path from any one of the source vertices in sources to every other vertex in graph G.

Parameters:

G - the digraph

sources - the source vertices

Throws:

IllegalArgumentException - if sources is null

IllegalArgumentException - if sources contains no vertices

IllegalArgumentException - unless each vertex v in sources satisfies 0 <= v < V

Method Detail

hasPathTo

public boolean hasPathTo(int v)

Is there a directed path from the source s (or sources) to vertex v?

Parameters:

v - the vertex

Returns:

true if there is a directed path, false otherwise

Throws:

IllegalArgumentException - unless 0 <= v < V

distTo

public int distTo(int v)

Returns the number of edges in a shortest path from the source s (or sources) to vertex v?

Parameters:

v - the vertex

Returns:

the number of edges in such a shortest path (or Integer.MAX_VALUE if there is no such path)

Throws:

IllegalArgumentException - unless 0 <= v < V

pathTo

public Iterable<Integer> pathTo(int v)

Returns a shortest path from s (or sources) to v, or null if no such path.

Parameters:

v - the vertex

Returns:

the sequence of vertices on a shortest path, as an Iterable

Throws:

IllegalArgumentException - unless 0 <= v < V

main

public static void main(String[] args)

Unit tests the BreadthFirstDirectedPaths data type.

Parameters:

args - the command-line arguments