edu.princeton.cs.algorithms

Class AcyclicLP

java.lang.Object

edu.princeton.cs.algorithms.AcyclicLP

public class AcyclicLP
extends Object

The AcyclicLP class represents a data type for solving the single-source longest paths problem in edge-weighted directed acyclic graphs (DAGs). The edge weights can be positive, negative, or zero.

This implementation uses a topological-sort based algorithm. The constructor takes time proportional to V + E, where V is the number of vertices and E is the number of edges. Afterwards, the distTo() and hasPathTo() methods take constant time and the pathTo() method takes time proportional to the number of edges in the longest path returned.

For additional documentation, see Section 4.4 of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.

Author:

Robert Sedgewick, Kevin Wayne

Constructor Summary

Constructors

Constructor and Description
AcyclicLP(EdgeWeightedDigraph G, int s) Computes a longest paths tree from s to every other vertex in the directed acyclic graph G.

Method Summary

Methods

Modifier and Type	Method and Description
double	distTo(int v) Returns the length of a longest path from the source vertex s to vertex v.
boolean	hasPathTo(int v) Is there a path from the source vertex s to vertex v?
static void	main(String[] args) Unit tests the AcyclicLP data type.
Iterable<DirectedEdge>	pathTo(int v) Returns a longest path from the source vertex s to vertex v.

Methods inherited from class java.lang.Object

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

Constructor Detail

AcyclicLP

public AcyclicLP(EdgeWeightedDigraph G,
         int s)

Computes a longest paths tree from s to every other vertex in the directed acyclic graph G.

Parameters:

G - the acyclic digraph

s - the source vertex

Throws:

IllegalArgumentException - if the digraph is not acyclic

IllegalArgumentException - unless 0 ≤ s ≤ V - 1

Method Detail

distTo

public double distTo(int v)

Returns the length of a longest path from the source vertex s to vertex v.

Parameters:

v - the destination vertex

Returns:

the length of a longest path from the source vertex s to vertex v; Double.NEGATIVE_INFINITY if no such path

hasPathTo

public boolean hasPathTo(int v)

Is there a path from the source vertex s to vertex v?

Parameters:

v - the destination vertex

Returns:

true if there is a path from the source vertex s to vertex v, and false otherwise

pathTo

public Iterable<DirectedEdge> pathTo(int v)

Returns a longest path from the source vertex s to vertex v.

Parameters:

v - the destination vertex

Returns:

a longest path from the source vertex s to vertex v as an iterable of edges, and null if no such path

main

public static void main(String[] args)

Unit tests the AcyclicLP data type.