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mis-plugin/src/main/groovy/com/eastwood/tools/plugins/mis/core/Digraph.java
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| package com.eastwood.tools.plugins.mis.core; | ||
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| import java.util.ArrayList; | ||
| import java.util.HashMap; | ||
| import java.util.LinkedList; | ||
| import java.util.List; | ||
| import java.util.Map; | ||
| import java.util.Queue; | ||
| import java.util.Stack; | ||
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|
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| /** | ||
| * An example class for directed graphs. The vertex type can be specified. | ||
| * There are no edge costs/weights. | ||
| * <p> | ||
| * Written for CS211, Nov 2006. | ||
| * | ||
| * @author Paul Chew | ||
| */ | ||
| public class Digraph<V> { | ||
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| /** | ||
| * The implementation here is basically an adjacency list, but instead | ||
| * of an array of lists, a Map is used to map each vertex to its list of | ||
| * adjacent vertices. | ||
| */ | ||
| private Map<V, List<V>> neighbors = new HashMap<V, List<V>>(); | ||
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| /** | ||
| * String representation of dependencyGraph. | ||
| */ | ||
| public String toString() { | ||
| StringBuffer s = new StringBuffer(); | ||
| for (V v : neighbors.keySet()) s.append("\n " + v + " -> " + neighbors.get(v)); | ||
| return s.toString(); | ||
| } | ||
|
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| /** | ||
| * Add a vertex to the dependencyGraph. Nothing happens if vertex is already in dependencyGraph. | ||
| */ | ||
| public void add(V vertex) { | ||
| if (neighbors.containsKey(vertex)) return; | ||
| neighbors.put(vertex, new ArrayList<V>()); | ||
| } | ||
|
|
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| /** | ||
| * True iff dependencyGraph contains vertex. | ||
| */ | ||
| public boolean contains(V vertex) { | ||
| return neighbors.containsKey(vertex); | ||
| } | ||
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| /** | ||
| * Add an edge to the dependencyGraph; if either vertex does not exist, it's added. | ||
| * This implementation allows the creation of multi-edges and self-loops. | ||
| */ | ||
| public void add(V from, V to) { | ||
| this.add(from); | ||
| this.add(to); | ||
| neighbors.get(from).add(to); | ||
| } | ||
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| /** | ||
| * Remove an edge from the dependencyGraph. Nothing happens if no such edge. | ||
| * | ||
| * @throws IllegalArgumentException if either vertex doesn't exist. | ||
| */ | ||
| public void remove(V from, V to) { | ||
| if (!(this.contains(from) && this.contains(to))) | ||
| throw new IllegalArgumentException("Nonexistent vertex"); | ||
| neighbors.get(from).remove(to); | ||
| } | ||
|
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| /** | ||
| * Report (as a Map) the out-degree of each vertex. | ||
| */ | ||
| public Map<V, Integer> outDegree() { | ||
| Map<V, Integer> result = new HashMap<V, Integer>(); | ||
| for (V v : neighbors.keySet()) result.put(v, neighbors.get(v).size()); | ||
| return result; | ||
| } | ||
|
|
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| /** | ||
| * Report (as a Map) the in-degree of each vertex. | ||
| */ | ||
| public Map<V, Integer> inDegree() { | ||
| Map<V, Integer> result = new HashMap<V, Integer>(); | ||
| for (V v : neighbors.keySet()) result.put(v, 0); // All in-degrees are 0 | ||
| for (V from : neighbors.keySet()) { | ||
| for (V to : neighbors.get(from)) { | ||
| result.put(to, result.get(to) + 1); // Increment in-degree | ||
| } | ||
| } | ||
| return result; | ||
| } | ||
|
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| /** | ||
| * Report (as a List) the topological sort of the vertices; null for no such sort. | ||
| */ | ||
| public List<V> topSort() { | ||
| Map<V, Integer> degree = inDegree(); | ||
| // Determine all vertices with zero in-degree | ||
| Stack<V> zeroVerts = new Stack<V>(); // Stack as good as any here | ||
| for (V v : degree.keySet()) { | ||
| if (degree.get(v) == 0) zeroVerts.push(v); | ||
| } | ||
| // Determine the topological order | ||
| List<V> result = new ArrayList<V>(); | ||
| while (!zeroVerts.isEmpty()) { | ||
| V v = zeroVerts.pop(); // Choose a vertex with zero in-degree | ||
| result.add(v); // Vertex v is next in topol order | ||
| // "Remove" vertex v by updating its neighbors | ||
| for (V neighbor : neighbors.get(v)) { | ||
| degree.put(neighbor, degree.get(neighbor) - 1); | ||
| // Remember any vertices that now have zero in-degree | ||
| if (degree.get(neighbor) == 0) zeroVerts.push(neighbor); | ||
| } | ||
| } | ||
| // Check that we have used the entire dependencyGraph (if not, there was a cycle) | ||
| if (result.size() != neighbors.size()) return null; | ||
| return result; | ||
| } | ||
|
|
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| /** | ||
| * True iff dependencyGraph is a dag (directed acyclic dependencyGraph). | ||
| */ | ||
| public boolean isDag() { | ||
| return topSort() != null; | ||
| } | ||
|
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||
| /** | ||
| * Report (as a Map) the bfs distance to each vertex from the start vertex. | ||
| * The distance is an Integer; the value null is used to represent infinity | ||
| * (implying that the corresponding node cannot be reached). | ||
| */ | ||
| public Map bfsDistance(V start) { | ||
| Map<V, Integer> distance = new HashMap<V, Integer>(); | ||
| // Initially, all distance are infinity, except start node | ||
| for (V v : neighbors.keySet()) distance.put(v, null); | ||
| distance.put(start, 0); | ||
| // Process nodes in queue order | ||
| Queue<V> queue = new LinkedList<V>(); | ||
| queue.offer(start); // Place start node in queue | ||
| while (!queue.isEmpty()) { | ||
| V v = queue.remove(); | ||
| int vDist = distance.get(v); | ||
| // Update neighbors | ||
| for (V neighbor : neighbors.get(v)) { | ||
| if (distance.get(neighbor) != null) continue; // Ignore if already done | ||
| distance.put(neighbor, vDist + 1); | ||
| queue.offer(neighbor); | ||
| } | ||
| } | ||
| return distance; | ||
| } | ||
|
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| // /** | ||
| // * Main program (for testing). | ||
| // */ | ||
| // public static void main (String[] args) { | ||
| // // Create a Graph with Integer nodes | ||
| // Digraph<Integer> graph = new Digraph<Integer>(); | ||
| // graph.add(0, 1); graph.add(0, 2); graph.add(0, 3); | ||
| // graph.add(1, 2); graph.add(1, 3); graph.add(2, 3); | ||
| // graph.add(2, 4); graph.add(4, 5); graph.add(5, 6); // Tetrahedron with tail | ||
| // System.out.println("The current dependencyGraph: " + graph); | ||
| // System.out.println("In-degrees: " + graph.inDegree()); | ||
| // System.out.println("Out-degrees: " + graph.outDegree()); | ||
| // System.out.println("A topological sort of the vertices: " + graph.topSort()); | ||
| // System.out.println("The dependencyGraph " + (graph.isDag()?"is":"is not") + " a dag"); | ||
| // System.out.println("BFS distances starting from " + 0 + ": " + graph.bfsDistance(0)); | ||
| // System.out.println("BFS distances starting from " + 1 + ": " + graph.bfsDistance(1)); | ||
| // System.out.println("BFS distances starting from " + 2 + ": " + graph.bfsDistance(2)); | ||
| // graph.add(4, 1); // Create a cycle | ||
| // System.out.println("Cycle created"); | ||
| // System.out.println("The current dependencyGraph: " + graph); | ||
| // System.out.println("In-degrees: " + graph.inDegree()); | ||
| // System.out.println("Out-degrees: " + graph.outDegree()); | ||
| // System.out.println("A topological sort of the vertices: " + graph.topSort()); | ||
| // System.out.println("The dependencyGraph " + (graph.isDag()?"is":"is not") + " a dag"); | ||
| // System.out.println("BFS distances starting from " + 2 + ": " + graph.bfsDistance(2)); | ||
| // } | ||
| } |
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