package self.learning.interview.coding;
import java.util.*;
public class ShortestPath {
/**
* Represents Station in the rail network. Each station is identified by unique name.
* Station is connected with other stations - this information is stored in the 'neighbours' field.
* Two station objects with the same name are equal therefore they are considered to be same station.
*/
private static class Station {
private String name;
private List<Station> neighbours;
Station(String name) {
this.name = name;
this.neighbours = new ArrayList<>(3);
}
String getName() {
return name;
}
void addNeighbour(Station v) {
this.neighbours.add(v);
}
List<Station> getNeighbours() {
return this.neighbours;
}
@Override
public boolean equals(Object obj) {
return obj instanceof Station && this.name.equals(((Station) obj).getName());
}
@Override
public int hashCode() {
return Objects.hash(this.name);
}
}
/**
* class TrainMap
* <p>
* Respresents whole rail network - consists of number of the Station objects.
* Stations in the map are bi-directionally connected. Distance between any 2 stations
* is of same constant distance unit. This implies that shortest distance between any
* 2 stations depends only on number of stations in between
*/
private static class TrainMap {
private HashMap<String, Station> stations;
TrainMap() {
this.stations = new HashMap<>();
}
TrainMap addStation(String name) {
Station s = new Station(name);
this.stations.putIfAbsent(name, s);
return this;
}
Station getStation(String name) {
return this.stations.get(name);
}
TrainMap connectStations(Station fromStation, Station toStation) {
if (fromStation == null) throw new IllegalArgumentException("From station is null");
if (toStation == null) throw new IllegalArgumentException("From station is null");
fromStation.addNeighbour(toStation);
toStation.addNeighbour(fromStation);
return this;
}
List<Station> shortestPath(final String from, final String to) {
final Station fromStation = this.getStation(from);
final Station toStation = this.getStation(to);
final Stack<Station> dfs = new Stack<>();
dfs.push(fromStation);
Station pathStation = null;
final List<Station> shortestPath = new ArrayList<>();
while (!dfs.empty()) {
pathStation = dfs.pop();
if (pathStation.getName().equalsIgnoreCase(toStation.getName())) {
}
dfs.addAll(pathStation.getNeighbours());
}
return Collections.emptyList();
}
static String convertPathToStringRepresentation(List<Station> path) {
if (path.isEmpty()) {
return "";
}
return path.stream().map(Station::getName).reduce((s1, s2) -> s1 + "->" + s2).get();
}
}
private static boolean doTestsPass() {
// todo: implement more tests, please
// feel free to make testing more elegant
TrainMap trainMap = new TrainMap();
trainMap.addStation("King's Cross St Pancras").addStation("Angel").addStation("Old Street").addStation("Moorgate")
.addStation("Farringdon").addStation("Barbican").addStation("Russel Square").addStation("Holborn")
.addStation("Chancery Lane").addStation("St Paul's").addStation("Bank");
trainMap.connectStations(trainMap.getStation("King's Cross St Pancras"), trainMap.getStation("Angel"))
.connectStations(trainMap.getStation("King's Cross St Pancras"), trainMap.getStation("Farringdon"))
.connectStations(trainMap.getStation("King's Cross St Pancras"), trainMap.getStation("Russel Square"))
.connectStations(trainMap.getStation("Russel Square"), trainMap.getStation("Holborn"))
.connectStations(trainMap.getStation("Holborn"), trainMap.getStation("Chancery Lane"))
.connectStations(trainMap.getStation("Chancery Lane"), trainMap.getStation("St Paul's"))
.connectStations(trainMap.getStation("St Paul's"), trainMap.getStation("Bank"))
.connectStations(trainMap.getStation("Angel"), trainMap.getStation("Old Street"))
.connectStations(trainMap.getStation("Old Street"), trainMap.getStation("Moorgate"))
.connectStations(trainMap.getStation("Moorgate"), trainMap.getStation("Bank"))
.connectStations(trainMap.getStation("Farringdon"), trainMap.getStation("Barbican"))
.connectStations(trainMap.getStation("Barbican"), trainMap.getStation("Moorgate"));
String solution = "King's Cross St Pancras->Russel Square->Holborn->Chancery Lane->St Paul's";
return solution.equals(TrainMap.convertPathToStringRepresentation(trainMap.shortestPath("King's Cross St Pancras", "St Paul's")));
}
public static void main(String[] args) {
if (doTestsPass()) {
System.out.println("All tests pass");
} else {
System.out.println("Tests fail.");
}
}
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// add dependencies here as below
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Java is a very popular general-purpose programming language, it is class-based and object-oriented. Java was developed by James Gosling at Sun Microsystems ( later acquired by Oracle) the initial release of Java was in 1995. Java 17 is the latest long-term supported version (LTS). As of today, Java is the world's number one server programming language with a 12 million developer community, 5 million students studying worldwide and it's #1 choice for the cloud development.
short x = 999; // -32768 to 32767
int x = 99999; // -2147483648 to 2147483647
long x = 99999999999L; // -9223372036854775808 to 9223372036854775807
float x = 1.2;
double x = 99.99d;
byte x = 99; // -128 to 127
char x = 'A';
boolean x = true;
When ever you want to perform a set of operations based on a condition If-Else is used.
if(conditional-expression) {
// code
} else {
// code
}
Example:
int i = 10;
if(i % 2 == 0) {
System.out.println("i is even number");
} else {
System.out.println("i is odd number");
}
Switch is an alternative to If-Else-If ladder and to select one among many blocks of code.
switch(<conditional-expression>) {
case value1:
// code
break; // optional
case value2:
// code
break; // optional
...
default:
//code to be executed when all the above cases are not matched;
}
For loop is used to iterate a set of statements based on a condition. Usually for loop is preferred when number of iterations is known in advance.
for(Initialization; Condition; Increment/decrement){
//code
}
While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.
while(<condition>){
// code
}
Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.
do {
// code
} while (<condition>);
Class is the blueprint of an object, which is also referred as user-defined data type with variables and functions. Object is a basic unit in OOP, and is an instance of the class.
class keyword is required to create a class.
class Mobile {
public: // access specifier which specifies that accessibility of class members
string name; // string variable (attribute)
int price; // int variable (attribute)
};
Mobile m1 = new Mobile();
public class Greeting {
static void hello() {
System.out.println("Hello.. Happy learning!");
}
public static void main(String[] args) {
hello();
}
}
Collection is a group of objects which can be represented as a single unit. Collections are introduced to bring a unified common interface to all the objects.
Collection Framework was introduced since JDK 1.2 which is used to represent and manage Collections and it contains:
This framework also defines map interfaces and several classes in addition to Collections.
| Collection | Description |
|---|---|
| Set | Set is a collection of elements which can not contain duplicate values. Set is implemented in HashSets, LinkedHashSets, TreeSet etc |
| List | List is a ordered collection of elements which can have duplicates. Lists are classified into ArrayList, LinkedList, Vectors |
| Queue | FIFO approach, while instantiating Queue interface you can either choose LinkedList or PriorityQueue. |
| Deque | Deque(Double Ended Queue) is used to add or remove elements from both the ends of the Queue(both head and tail) |
| Map | Map contains key-values pairs which don't have any duplicates. Map is implemented in HashMap, TreeMap etc. |