edu.princeton.cs.algs4

Class BreadthFirstPaths

java.lang.Object

edu.princeton.cs.algs4.BreadthFirstPaths

public class BreadthFirstPaths
extends java.lang.Object

The BreadthFirstPaths class represents a data type for finding shortest paths (number of edges) from a source vertex s (or a set of source vertices) to every other vertex in an undirected graph.

This implementation uses breadth-first search. The constructor takes time proportional to V + E, where V is the number of vertices and E is the number of edges. Each call to distTo(int) and hasPathTo(int) takes constant time; each call to pathTo(int) takes time proportional to the length of the path. It uses extra space (not including the graph) proportional to V.

For additional documentation, see Section 4.1 of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.

Constructor Summary

Constructors

Constructor and Description
BreadthFirstPaths(Graph G, int s) Computes the shortest path between the source vertex s and every other vertex in the graph G.
BreadthFirstPaths(Graph G, java.lang.Iterable<java.lang.Integer> sources) Computes the shortest path between any one of the source vertices in sources and every other vertex in graph G.

Method Summary

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

Methods inherited from class java.lang.Object

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

Constructor Detail

BreadthFirstPaths

public BreadthFirstPaths(Graph G,
                         int s)

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

Parameters:

G - the graph

s - the source vertex

Throws:

java.lang.IllegalArgumentException - unless 0 <= s < V

BreadthFirstPaths

public BreadthFirstPaths(Graph G,
                         java.lang.Iterable<java.lang.Integer> sources)

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

Parameters:

G - the graph

sources - the source vertices

Throws:

java.lang.IllegalArgumentException - unless 0 <= s < V for each vertex s in sources

Method Detail

hasPathTo

public boolean hasPathTo(int v)

Is there a path between the source vertex s (or sources) and vertex v?

Parameters:

v - the vertex

Returns:

true if there is a path, and false otherwise

Throws:

java.lang.IllegalArgumentException - unless 0 <= v < V

distTo

public int distTo(int v)

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

Parameters:

v - the vertex

Returns:

the number of edges in a shortest path

Throws:

java.lang.IllegalArgumentException - unless 0 <= v < V

pathTo

public java.lang.Iterable<java.lang.Integer> pathTo(int v)

Returns a shortest path between the source vertex s (or sources) and v, or null if no such path.

Parameters:

v - the vertex

Returns:

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

Throws:

java.lang.IllegalArgumentException - unless 0 <= v < V

main

public static void main(java.lang.String[] args)

Unit tests the BreadthFirstPaths data type.

Parameters:

args - the command-line arguments