# Answered Essay: Work with Dijkstra's single-source shortest path algorithm.

```Objective:

Work with Dijkstra's single-source shortest path algorithm.

Overview:

In this project you will use Dijkstra's algorithm to find route information
between two airports chosen by the user.  The user will be shown a route that
results in the lowest price.

Details:

Write a Java program that lets the user choose two airports and finds
the route that has the least price.

Your program should read the airports.txt file that is posted, or any file
having the same format.
It should then prompt the user to enter two airports.

Dijkstra's algorithm should be run to find the cheapest route.  The price,
number of connections, and actual route should be shown.

The user should be able to continue checking routes until no more routes are requested.

You are expected to write Dijkstra's algorithm yourself following the pseudocode
found in both the slides and in the textbook.  You can use the Vertex class and
printPath found in the textbook if you wish.
You may not use code for Dijkstra's algorithm found from other sources.

Your output should match the sample output below:

Sample output:

Enter departure airport:  DFW
Enter arrival airport:    SFO

By price:
Price:       1100
Connections: 1
Route:       DFW -> LAX -> SFO

Check another route (Y/N)?
```

AIRPORTS.TXT

ATL BOS 250 DFW 250 MOB 59

```AUS  DFW 59  HOU 59  SAT 59
BOS  ATL 250  DFW 250
DFW  ATL 250  AUS 59  BOS 250  HOU 128  LAX 1000  LIT 59  MSY 128  OKC 59  SHV 59  SFO 1200
HOU  AUS 59  DFW 128  SAT 59
LAX  DFW 1000  SFO 100
LIT  DFW 59
MOB  ATL 59
MSY  DFW 128
OKC  DFW 59
SAT  AUS 59  HOU 59
SFO  DFW 1200  LAX 100
SHV  DFW 59
```

Dijkstra.java

import java.io.File;

import java.io.FileNotFoundException;

import java.util.HashMap;

import java.util.Iterator;

import java.util.NoSuchElementException;

import java.util.PriorityQueue;

import java.util.Scanner;

import java.util.Set;

public class Dijkstra {

static HashMap<String, Vertex> mapvertex = new HashMap<String, Vertex>();

StringBuilder route = new StringBuilder();

public void dijkstra(Vertex departure, String arrival) {

Set<String> airportNames = mapvertex.keySet();

Iterator<String> airportIterator = airportNames.iterator();

while (airportIterator.hasNext()) {

Vertex vertex = mapvertex.get(airportIterator.next());

vertex.setKnown(false);

vertex.setCost(0);

vertex.setIsInfinity(true);

vertex.setPrevVertex(null);

}

departure.setIsInfinity(false);

Vertex vertex = departure;

vertex.setIsInfinity(false);

boolean arrivalFound = false;

PriorityQueue<Vertex> travvertx = new PriorityQueue<>();

for (;;) {

try {

vertex = travvertx.remove();

} catch (NoSuchElementException nsee) {

if (vertex == departure) {

} else {

break;

}

}

if (vertex == null) {

break;

}

while (iterator.hasNext()) {

int cost = vertex.getCost() + adjVertex.getCost();

} else {

}

}

}

}

}

vertex.setKnown(true);

}

}

public int printPath(Vertex departure, Vertex arrival) {

if (arrival == departure) {

route.append(arrival.getName() + ” -> “);

return -1;

} else {

int numberOfConnections = 1 + printPath(departure, arrival.getPrevVertex());

route.append(arrival.getName() + ” -> “);

return numberOfConnections;

}

}

public static void main(String[] args) throws FileNotFoundException {

File airports = new File(“Airports.txt”);

Scanner sc1 = new Scanner(airports);

while (sc1.hasNext()) {

String airportDetail = sc1.nextLine();

String[] splitString = airportDetail.split(” “);

Vertex airport = new Vertex(splitString[0]);

mapvertex.put(splitString[0], airport);

}

sc1 = new Scanner(airports);

while (sc1.hasNext()) {

String airportDetail = sc1.nextLine();

String[] splitString = airportDetail.split(” “);

Vertex airport = mapvertex.get(splitString[0]);

for (int j = 1; j < splitString.length; j++) {

String[] subStrings = splitString[j].split(” “);

int cost = Integer.parseInt(subStrings[1]);

}

}

while (true) {

Dijkstra dij = new Dijkstra();

Scanner sc = new Scanner(System.in);

System.out.print(“Enter Departure Airport: “);

String departure = sc.next().toUpperCase();

System.out.print(“Enter Arrival Airport: “);

String arrival = sc.next().toUpperCase();

Vertex depvertx = mapvertex.get(departure);

Vertex arrvertx = mapvertex.get(arrival);

System.out.println(“”);

dij.dijkstra(depvertx, arrival);

System.out.println(“By Price:”);

System.out.println(“”);

int numberOfConnections = dij.printPath(depvertx, arrvertx);

System.out.println(“Price : ” + arrvertx.getCost());

System.out.println(“Connection(s): ” + numberOfConnections);

dij.route.toString();

System.out.println(“Route : ” + dij.route.substring(0, dij.route.length() – 4));

System.out.println(“”);

System.out.println(“Check Another Route? (Y/N)”);

if (sc.next().toUpperCase().equals(“N”)) {

break;

}

}

}

}

Vertex.java

public class Vertex implements Comparable<Vertex> {

private String name;

private int cost;

private boolean known;

private boolean isInfinity;

private Vertex prevVertex;

public Vertex(String name) {

this.name = name;

this.cost = 0;

this.known = false;

this.isInfinity = true;

this.prevVertex = null;

}

}

}

public String getName() {

return this.name;

}

public int getCost() {

return this.cost;

}

public void setCost(int cost) {

this.cost = cost;

}

public boolean getKnown() {

return this.known;

}

public void setKnown(boolean known) {

this.known = known;

}

public boolean getIsInfinity() {

return this.isInfinity;

}

public void setIsInfinity(boolean isInfinity) {

this.isInfinity = isInfinity;

}

public Vertex getPrevVertex() {

return this.prevVertex;

}

public void setPrevVertex(Vertex prevVertex) {

this.prevVertex = prevVertex;

}

public int compareTo(Vertex vertex) {

return this.cost – vertex.getCost();

}

public String toString() {

return this.name;

}

}

private Vertex vertex;

private int cost;

public AdjacentVertex(Vertex vertex, int cost) {

this.vertex = vertex;

this.cost = cost;

}

public Vertex getVertex() {

return this.vertex;

}

public void setVertex(Vertex vertex) {

this.vertex = vertex;

}

public int getCost() {

return this.cost;

}

public void setCost(int cost) {

this.cost = cost;

}

}

Sample Output: –

Enter Departure Airport: DFW
Enter Arrival Airport: SFO

By Price:

Price : 1100
Connection(s): 1
Route : DFW -> LAX -> SFO

Check Another Route? (Y/N)
Y
Enter Departure Airport: ATL
Enter Arrival Airport: AUS

By Price:

Price : 309
Connection(s): 1
Route : ATL -> DFW -> AUS

Check Another Route? (Y/N)
Y
Enter Departure Airport: MOB
Enter Arrival Airport: DFW

By Price:

Price : 309
Connection(s): 1
Route : MOB -> ATL -> DFW

Check Another Route? (Y/N)
N

Pages (550 words)
Approximate price: -

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