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| 1 | +package backtracking; |
| 2 | + |
| 3 | +import java.util.HashSet; |
| 4 | +import java.util.Stack; |
| 5 | + |
| 6 | +/** |
| 7 | + * given a few flights and a starting point - print if you can connect them all together into a journey |
| 8 | + * <p> |
| 9 | + * a Flight is just an object that has a Starting point and an Ending point |
| 10 | + */ |
| 11 | + |
| 12 | +/** |
| 13 | + * Dynamic programming tips: |
| 14 | + * |
| 15 | + * Can I construct a mini problem with a solution |
| 16 | + * can I verify if that solution is valid or not |
| 17 | + * Can I say when the full problem is solved |
| 18 | + */ |
| 19 | + |
| 20 | +// in this case: |
| 21 | +// mini problem is just using less flights |
| 22 | +// is_valid would check if I am at an airport that I can't fly off from and there are more flights I have yet to board |
| 23 | +// full problem is solved when I have used all flights |
| 24 | +public class FlightItinerary { |
| 25 | + |
| 26 | + |
| 27 | + public static void addFlights(String startPoint, HashSet<Flight> flights, Stack<Flight> itinerary) { |
| 28 | + if (flights.isEmpty()) { |
| 29 | + //yey we have made a journey with everything |
| 30 | + return; |
| 31 | + } |
| 32 | + |
| 33 | + HashSet<Flight> expensiveSolution = new HashSet<>(flights); |
| 34 | + |
| 35 | + for (Flight i : flights) { |
| 36 | + if (startPoint.equals(i.start)) { |
| 37 | + itinerary.push(i); |
| 38 | + expensiveSolution.remove(i); |
| 39 | + |
| 40 | + //if valid so far try adding the next flight |
| 41 | + if (isValid(i.end, expensiveSolution)) { |
| 42 | + addFlights(i.end, expensiveSolution, itinerary); |
| 43 | + } else { |
| 44 | + |
| 45 | + itinerary.pop(); |
| 46 | + expensiveSolution.add(i); |
| 47 | + } |
| 48 | + } |
| 49 | + } |
| 50 | + } |
| 51 | + |
| 52 | + public static boolean isValid(String startPoint, HashSet<Flight> flights) { |
| 53 | + if (flights.isEmpty()) |
| 54 | + return true; |
| 55 | + for (Flight i : flights) { |
| 56 | + if (startPoint.equals(i.start)) { |
| 57 | + return true; |
| 58 | + } |
| 59 | + } |
| 60 | + return false; |
| 61 | + } |
| 62 | + |
| 63 | + public static void main(String[] args) { |
| 64 | + |
| 65 | + Flight f1 = new Flight("HNL", "AKL"); |
| 66 | + Flight f2 = new Flight("YUL", "ORD"); |
| 67 | + Flight f3 = new Flight("ORD", "SFO"); |
| 68 | + Flight f4 = new Flight("SFO", "HNL"); |
| 69 | + |
| 70 | + |
| 71 | + Flight f5 = new Flight("AKL", "ORD"); |
| 72 | + Flight f6 = new Flight("ORD", "YUL"); |
| 73 | + |
| 74 | + String startingAirport = "YUL"; |
| 75 | + |
| 76 | + HashSet<Flight> flights = new HashSet<>(); |
| 77 | + Stack<Flight> itinerary = new Stack<>(); |
| 78 | + |
| 79 | + flights.add(f1); |
| 80 | + flights.add(f2); |
| 81 | + flights.add(f3); |
| 82 | + flights.add(f4); |
| 83 | + |
| 84 | + |
| 85 | + flights.add(f5); |
| 86 | + flights.add(f6); |
| 87 | + |
| 88 | + addFlights("YUL", flights, itinerary); |
| 89 | + |
| 90 | + itinerary.stream().forEach(e -> System.out.print(e.start + " -> " + e.end + " ")); |
| 91 | + } |
| 92 | + |
| 93 | + private static class Flight { |
| 94 | + String start; |
| 95 | + String end; |
| 96 | + |
| 97 | + public Flight(String start, String end) { |
| 98 | + this.start = start; |
| 99 | + this.end = end; |
| 100 | + } |
| 101 | + } |
| 102 | +} |
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