Monday, 27 February 2017

Chapter 29 Exercise 9, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

29.9 (Find a minimum spanning tree) Write a program that reads a connected graph from a file and displays its minimum spanning tree. The first line in the file
contains a number that indicates the number of vertices ( n ). The vertices are
labeled as 0 , 1 , ..., n-1 . Each subsequent line describes the edges in the form
of u1, v1, w1 | u2, v2, w2 | ... . Each triplet in this form describes
an edge and its weight. Figure 29.24 shows an example of the file for the cor-
responding graph. Note that we assume the graph is undirected. If the graph has
an edge ( u , v ), it also has an edge ( v , u ). Only one edge is represented in the
file. When you construct a graph, both edges need to be added.
Your program should prompt the user to enter the name of the file, read data from the file, create an instance g of WeightedGraph , invoke g.printWeightedEdges()
to display all edges, invoke getMinimumSpanningTree() to obtain an instance
tree of WeightedGraph.MST , invoke tree.getTotalWeight() to display the
weight of the minimum spanning tree, and invoke tree.printTree() to display
the tree.

(Hint: Use new WeightedGraph(list, numberOfVertices) to create
a graph, where list contains a list of WeightedEdge objects. Use new
WeightedEdge(u, v, w) to create an edge. Read the first line to get the number of vertices. Read each subsequent line into a string s and use s.split("[\\|]")
to extract the triplets. For each triplet, use triplet.split("[,]") to extract
vertices and weight.)

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Scanner;

public class Exercise09 {

public static void main(String[] args) throws FileNotFoundException {
System.out.print("Enter a file name: ");
@SuppressWarnings("resource")
Scanner inputFileName = new Scanner(System.in);
String fileName = inputFileName.nextLine();
Scanner inputGraph = new Scanner(new File(fileName));
int numberOfVertices = inputGraph.nextInt();
inputGraph.nextLine();
System.out.println("The number of vertices is " + numberOfVertices);
ArrayList<Integer> vertices = new ArrayList<>();
for (int i = 0; i < numberOfVertices; i++) {
}
ArrayList<WeightedEdge> edges = new ArrayList<>();
while(inputGraph.hasNextLine()) {
String nextLine = inputGraph.nextLine();
nextLine = nextLine.replaceAll(",", "");
nextLine = nextLine.replaceAll("\\|", "");
Scanner inputVertic = new Scanner(nextLine);
while(inputVertic.hasNext()) {
int u = inputVertic.nextInt();
int v = inputVertic.nextInt();
double weight = inputVertic.nextDouble();
}
inputVertic.close();
}
inputGraph.close();
WeightedGraph<Integer> graph = new WeightedGraph<>(edges, vertices);
graph.printWeightedEdges();

WeightedGraph<Integer>.MST tree = graph.getMinimumSpanningTree();
System.out.println("Total weight is " + tree.getTotalWeight());
tree.printTree();

}

static class WeightedGraph<V> extends AbstractGraph<V> {
private List<PriorityQueue<WeightedEdge>> queues = new ArrayList<PriorityQueue<WeightedEdge>>();

/** Construct a WeightedGraph from edges and vertices in arrays */
public WeightedGraph() {
}

/** Construct a WeightedGraph from edges and vertices in arrays */
public WeightedGraph(int[][] edges, V[] vertices) {
super(edges, vertices);
createQueues(edges, vertices.length);
}

/** Construct a WeightedGraph from edges and vertices in List */
public WeightedGraph(int[][] edges, int numberOfVertices) {
super(edges, numberOfVertices);
createQueues(edges, numberOfVertices);
}

/** Construct a WeightedGraph for vertices 0, 1, 2 and edge list */
@SuppressWarnings({ "rawtypes", "unchecked" })
public WeightedGraph(List<WeightedEdge> edges, List<V> vertices) {
super((List) edges, vertices);
createQueues(edges, vertices.size());
}

/** Construct a WeightedGraph from vertices 0, 1, and edge array */
@SuppressWarnings({ "rawtypes", "unchecked" })
public WeightedGraph(List<WeightedEdge> edges, int numberOfVertices) {
super((List) edges, numberOfVertices);
createQueues(edges, numberOfVertices);
}

/** Create priority adjacency lists from edge arrays */
private void createQueues(int[][] edges, int numberOfVertices) {
for (int i = 0; i < numberOfVertices; i++) {
queues.add(new PriorityQueue<WeightedEdge>()); // Create a queue
}

for (int i = 0; i < edges.length; i++) {
int u = edges[i][0];
int v = edges[i][1];
int weight = edges[i][2];
// Insert an edge into the queue
queues.get(u).offer(new WeightedEdge(u, v, weight));
}
}

/** Create priority adjacency lists from edge lists */
private void createQueues(List<WeightedEdge> edges, int numberOfVertices) {
for (int i = 0; i < numberOfVertices; i++) {
queues.add(new PriorityQueue<WeightedEdge>()); // Create a queue
}

for (WeightedEdge edge : edges) {
queues.get(edge.u).offer(edge); // Insert an edge into the queue
}
}

/** Display edges with weights */
public void printWeightedEdges() {
for (int i = 0; i < queues.size(); i++) {
System.out.print(getVertex(i) + " (" + i + "): ");
for (WeightedEdge edge : queues.get(i)) {
System.out.print("(" + edge.u + ", " + edge.v + ", "
+ edge.weight + ") ");
}
System.out.println();
}
}

/** Get the edges from the weighted graph */
public List<PriorityQueue<WeightedEdge>> getWeightedEdges() {
return queues;
}

/** Clears the weighted graph */
public void clear() {
vertices.clear();
neighbors.clear();
queues.clear();
}

/** Add vertices to the weighted graph */
}

/** Add edges to the weighted graph */
public void addEdge(int u, int v, double weight) {
}

/** Get a minimum spanning tree rooted at vertex 0 */
public MST getMinimumSpanningTree() {
return getMinimumSpanningTree(0);
}

/** Get a minimum spanning tree rooted at a specified vertex */
public MST getMinimumSpanningTree(int startingVertex) {
List<Integer> T = new ArrayList<Integer>();
// T initially contains the startingVertex;

int numberOfVertices = vertices.size(); // Number of vertices
int[] parent = new int[numberOfVertices]; // Parent of a vertex
// Initially set the parent of all vertices to -1
for (int i = 0; i < parent.length; i++)
parent[i] = -1;
double totalWeight = 0; // Total weight of the tree thus far

// Clone the priority queue, so to keep the original queue intact
List<PriorityQueue<WeightedEdge>> queues = deepClone(this.queues);

// All vertices are found?
while (T.size() < numberOfVertices) {
// Search for the vertex with the smallest edge adjacent to
// a vertex in T
int v = -1;
double smallestWeight = Double.MAX_VALUE;
for (int u : T) {
while (!queues.get(u).isEmpty()
&& T.contains(queues.get(u).peek().v)) {
// Remove the edge from queues[u] if the adjacent
// vertex of u is already in T
queues.get(u).remove();
}

if (queues.get(u).isEmpty()) {
continue; // Consider the next vertex in T
}

// Current smallest weight on an edge adjacent to u
WeightedEdge edge = queues.get(u).peek();
if (edge.weight < smallestWeight) {
v = edge.v;
smallestWeight = edge.weight;
// If v is added to the tree, u will be its parent
parent[v] = u;
}
} // End of for

if (v != -1)
else
break; // The tree is not connected, a partial MST is found

totalWeight += smallestWeight;
} // End of while

return new MST(startingVertex, parent, T, totalWeight);
}

/** Clone an array of queues */
private List<PriorityQueue<WeightedEdge>> deepClone(
List<PriorityQueue<WeightedEdge>> queues) {
List<PriorityQueue<WeightedEdge>> copiedQueues = new ArrayList<PriorityQueue<WeightedEdge>>();

for (int i = 0; i < queues.size(); i++) {
for (WeightedEdge e : queues.get(i)) {
}
}

return copiedQueues;
}

/** MST is an inner class in WeightedGraph */
public class MST extends Tree {
private double totalWeight; // Total weight of all edges in the tree

public MST(int root, int[] parent, List<Integer> searchOrder,
double totalWeight) {
super(root, parent, searchOrder);
this.totalWeight = totalWeight;
}

public double getTotalWeight() {
}
}

/** Find single source shortest paths */
public ShortestPathTree getShortestPath(int sourceVertex) {
// T stores the vertices whose path found so far
List<Integer> T = new ArrayList<Integer>();
// T initially contains the sourceVertex;

// vertices is defined in AbstractGraph
int numberOfVertices = vertices.size();

// parent[v] stores the previous vertex of v in the path
int[] parent = new int[numberOfVertices];
parent[sourceVertex] = -1; // The parent of source is set to -1

// cost[v] stores the cost of the path from v to the source
double[] cost = new double[numberOfVertices];
for (int i = 0; i < cost.length; i++) {
cost[i] = Double.MAX_VALUE; // Initial cost set to infinity
}
cost[sourceVertex] = 0; // Cost of source is 0

// Get a copy of queues
List<PriorityQueue<WeightedEdge>> queues = deepClone(this.queues);

// Expand T
while (T.size() < numberOfVertices) {
int v = -1; // Vertex to be determined
double smallestCost = Double.MAX_VALUE; // Set to infinity
for (int u : T) {
while (!queues.get(u).isEmpty()
&& T.contains(queues.get(u).peek().v)) {
queues.get(u).remove(); // Remove the vertex in queue
// for u
}

if (queues.get(u).isEmpty()) {
// All vertices adjacent to u are in T
continue;
}

WeightedEdge e = queues.get(u).peek();
if (cost[u] + e.weight < smallestCost) {
v = e.v;
smallestCost = cost[u] + e.weight;
// If v is added to the tree, u will be its parent
parent[v] = u;
}
} // End of for

cost[v] = smallestCost;
} // End of while

// Create a ShortestPathTree
return new ShortestPathTree(sourceVertex, parent, T, cost);
}

/** ShortestPathTree is an inner class in WeightedGraph */
public class ShortestPathTree extends Tree {
private double[] cost; // cost[v] is the cost from v to source

/** Construct a path */
public ShortestPathTree(int source, int[] parent,
List<Integer> searchOrder, double[] cost) {
super(source, parent, searchOrder);
this.cost = cost;
}

/** Return the cost for a path from the root to vertex v */
public double getCost(int v) {
return cost[v];
}

/** Print paths from all vertices to the source */
public void printAllPaths() {
System.out.println("All shortest paths from "
+ vertices.get(getRoot()) + " are:");
for (int i = 0; i < cost.length; i++) {
printPath(i); // Print a path from i to the source
System.out.println("(cost: " + cost[i] + ")"); // Path cost
}
}
}
}

static class WeightedEdge extends AbstractGraph.Edge implements Comparable<WeightedEdge> {
public double weight; // The weight on edge (u, v)

/** Create a weighted edge on (u, v) */
public WeightedEdge(int u, int v, double weight) {
super(u, v);
this.weight = weight;
}

/** Compare two edges on weights */
public int compareTo(WeightedEdge edge) {
if (weight > edge.weight) {
return 1;
} else if (weight == edge.weight) {
return 0;
} else {
return -1;
}
}

@Override
public boolean equals(Object obj) {
if (obj instanceof WeightedEdge) {
WeightedEdge that = (WeightedEdge)obj;
return (u == that.u) && (v == that.v) && (weight == that.weight);
} else {
return false;
}
}

@Override
public String toString() {
return "(" + u + ", " + v + ", " + weight + ")";
}
}

static abstract class AbstractGraph<V> implements Graph<V> {
protected List<V> vertices = new ArrayList<V>(); // Store vertices
protected List<List<Integer>> neighbors = new ArrayList<List<Integer>>(); // Adjacency
// lists

/** Construct an empty graph */
protected AbstractGraph() {
}

/** Construct a graph from edges and vertices stored in arrays */
protected AbstractGraph(int[][] edges, V[] vertices) {
for (int i = 0; i < vertices.length; i++)

}

/** Construct a graph from edges and vertices stored in List */
protected AbstractGraph(List<Edge> edges, List<V> vertices) {
for (int i = 0; i < vertices.size(); i++)

}

/** Construct a graph for integer vertices 0, 1, 2 and edge list */
@SuppressWarnings("unchecked")
protected AbstractGraph(List<Edge> edges, int numberOfVertices) {
for (int i = 0; i < numberOfVertices; i++)
vertices.add((V) (new Integer(i))); // vertices is {0, 1, ...}

}

/** Construct a graph from integer vertices 0, 1, and edge array */
@SuppressWarnings("unchecked")
protected AbstractGraph(int[][] edges, int numberOfVertices) {
for (int i = 0; i < numberOfVertices; i++)
vertices.add((V) (new Integer(i))); // vertices is {0, 1, ...}

}

/** Create adjacency lists for each vertex */
private void createAdjacencyLists(int[][] edges, int numberOfVertices) {
for (int i = 0; i < numberOfVertices; i++) {
}

for (int i = 0; i < edges.length; i++) {
int u = edges[i][0];
int v = edges[i][1];
}
}

/** Create adjacency lists for each vertex */
private void createAdjacencyLists(List<Edge> edges, int numberOfVertices) {
// Create a linked list for each vertex
for (int i = 0; i < numberOfVertices; i++) {
}

for (Edge edge : edges) {
}
}

public boolean isCyclic() {
for (int i = 0; i < vertices.size(); i++) {
if(isCyclic(i)) {
return true;
}
}
return false;
}

private boolean isCyclic(int v) {
List<Integer> searchOrder = new ArrayList<Integer>();
int[] parent = new int[vertices.size()];
for (int i = 0; i < parent.length; i++) {
parent[i] = -1;
}

boolean[] isVisited = new boolean[vertices.size()];

return isCyclic(v, v, parent, searchOrder, isVisited);

}

private boolean isCyclic(int first, int v, int[] parent, List<Integer> searchOrder, boolean[] isVisited) {
isVisited[v] = true;

for (int i : neighbors.get(v)) {
if (!isVisited[i]) {
parent[i] = v;
int[] newParent = java.util.Arrays.copyOf(parent, parent.length);
boolean[] newIsVisited = java.util.Arrays.copyOf(isVisited, parent.length);
@SuppressWarnings("unchecked")
List<Integer> newSearchOrder = (List<Integer>) ((ArrayList<Integer>)searchOrder).clone();
if(isCyclic(first, i, newParent, newSearchOrder, newIsVisited)) {
return true;
}
} else if(first == i) {
if(searchOrder.size() > 2) {
return true;
}
}
}
return false;
}

@Override
/** Return the number of vertices in the graph */
public int getSize() {
return vertices.size();
}

@Override
/** Return the vertices in the graph */
public List<V> getVertices() {
return vertices;
}

@Override
/** Return the object for the specified vertex */
public V getVertex(int index) {
return vertices.get(index);
}

@Override
/** Return the index for the specified vertex object */
public int getIndex(V v) {
return vertices.indexOf(v);
}

@Override
/** Return the neighbors of the specified vertex */
public List<Integer> getNeighbors(int index) {
return neighbors.get(index);
}

@Override
/** Return the degree for a specified vertex */
public int getDegree(int v) {
return neighbors.get(v).size();
}

@Override
/** Print the edges */
public void printEdges() {
for (int u = 0; u < neighbors.size(); u++) {
System.out.print(getVertex(u) + " (" + u + "): ");
for (int j = 0; j < neighbors.get(u).size(); j++) {
System.out.print("(" + u + ", " + neighbors.get(u).get(j)
+ ") ");
}
System.out.println();
}
}

@Override
/** Clear graph */
public void clear() {
vertices.clear();
neighbors.clear();
}

@Override
/** Add a vertex to the graph */
}

@Override
/** Add an edge to the graph */
public void addEdge(int u, int v) {
}

/** Edge inner class inside the AbstractGraph class */
public static class Edge {
public int u; // Starting vertex of the edge
public int v; // Ending vertex of the edge

/** Construct an edge for (u, v) */
public Edge(int u, int v) {
this.u = u;
this.v = v;
}
}

@Override
/** Obtain a DFS tree starting from vertex v */
/** To be discussed in Section 27.6 */
public Tree dfs(int v) {
List<Integer> searchOrder = new ArrayList<Integer>();
int[] parent = new int[vertices.size()];
for (int i = 0; i < parent.length; i++)
parent[i] = -1; // Initialize parent[i] to -1

// Mark visited vertices
boolean[] isVisited = new boolean[vertices.size()];

// Recursively search
dfs(v, parent, searchOrder, isVisited);

// Return a search tree
return new Tree(v, parent, searchOrder);
}

/** Recursive method for DFS search */
private void dfs(int v, int[] parent, List<Integer> searchOrder,
boolean[] isVisited) {
// Store the visited vertex
isVisited[v] = true; // Vertex v visited

for (int i : neighbors.get(v)) {
if (!isVisited[i]) {
parent[i] = v; // The parent of vertex i is v
dfs(i, parent, searchOrder, isVisited); // Recursive search
}
}
}

@Override
/** Starting bfs search from vertex v */
/** To be discussed in Section 27.7 */
public Tree bfs(int v) {
List<Integer> searchOrder = new ArrayList<Integer>();
int[] parent = new int[vertices.size()];
for (int i = 0; i < parent.length; i++)
parent[i] = -1; // Initialize parent[i] to -1

// used
// as
// a
// queue
boolean[] isVisited = new boolean[vertices.size()];
queue.offer(v); // Enqueue v
isVisited[v] = true; // Mark it visited

while (!queue.isEmpty()) {
int u = queue.poll(); // Dequeue to u
for (int w : neighbors.get(u)) {
if (!isVisited[w]) {
queue.offer(w); // Enqueue w
parent[w] = u; // The parent of w is u
isVisited[w] = true; // Mark it visited
}
}
}

return new Tree(v, parent, searchOrder);
}

/** Tree inner class inside the AbstractGraph class */
/** To be discussed in Section 27.5 */
public class Tree {
private int root; // The root of the tree
private int[] parent; // Store the parent of each vertex
private List<Integer> searchOrder; // Store the search order

/** Construct a tree with root, parent, and searchOrder */
public Tree(int root, int[] parent, List<Integer> searchOrder) {
this.root = root;
this.parent = parent;
this.searchOrder = searchOrder;
}

/** Return the root of the tree */
public int getRoot() {
return root;
}

/** Return the parent of vertex v */
public int getParent(int v) {
return parent[v];
}

/** Return an array representing search order */
public List<Integer> getSearchOrder() {
return searchOrder;
}

/** Return number of vertices found */
public int getNumberOfVerticesFound() {
return searchOrder.size();
}

/** Return the path of vertices from a vertex to the root */
public List<V> getPath(int index) {
ArrayList<V> path = new ArrayList<V>();

do {
index = parent[index];
} while (index != -1);

return path;
}

/** Print a path from the root to vertex v */
public void printPath(int index) {
List<V> path = getPath(index);
System.out.print("A path from " + vertices.get(root) + " to "
+ vertices.get(index) + ": ");
for (int i = path.size() - 1; i >= 0; i--)
System.out.print(path.get(i) + " ");
}

/** Print the whole tree */
public void printTree() {
System.out.println("Root is: " + vertices.get(root));
System.out.print("Edges: ");
for (int i = 0; i < parent.length; i++) {
if (parent[i] != -1) {
// Display an edge
System.out.print("(" + vertices.get(parent[i]) + ", "
+ vertices.get(i) + ") ");
}
}
System.out.println();
}
}
}

interface Graph<V> {
/** Return the number of vertices in the graph */
public int getSize();

/** Return the vertices in the graph */
public java.util.List<V> getVertices();

/** Return the object for the specified vertex index */
public V getVertex(int index);

/** Return the index for the specified vertex object */
public int getIndex(V v);

/** Return the neighbors of vertex with the specified index */
public java.util.List<Integer> getNeighbors(int index);

/** Return the degree for a specified vertex */
public int getDegree(int v);

/** Print the edges */
public void printEdges();

/** Clear graph */
public void clear();

/** Add a vertex to the graph */

/** Add an edge to the graph */
public void addEdge(int u, int v);

/** Obtain a depth-first search tree */
public AbstractGraph<V>.Tree dfs(int v);

/** Obtain a breadth-first search tree */
public AbstractGraph<V>.Tree bfs(int v);
}

}