Part four

src/flashcards/Main.java

@@ -1,7 +1,44 @@
 package flashcards;
 
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Scanner;
+
 public class Main {
-    public static void main(String[] args) {
-        System.out.print("Hello world!");
+
+  public static void main(String[] args) {
+    try (Scanner scanner = new Scanner(System.in)) {
+      System.out.printf("Input the number of cards:\n");
+
+      int numCards = Integer.parseInt(scanner.nextLine());
+
+      Map<String, String> cardToDefinition = new LinkedHashMap<>();
+      Map<String, String> definitionToCard = new LinkedHashMap<>();
+
+      for (int i = 0; i < numCards; i++) {
+        System.out.printf("The card #%d:\n", i + 1);
+        String card = scanner.nextLine();
+        System.out.printf("The definition of the card #%d:\n", i + 1);
+        String definition = scanner.nextLine();
+        cardToDefinition.put(card, definition);
+        definitionToCard.put(definition, card);
+      }
+
+      for (String card : cardToDefinition.keySet()) {
+        System.out.printf("Print the definition of \"%s\":\n", card);
+        String guess = scanner.nextLine();
+        if (definitionToCard.containsKey(guess) && cardToDefinition.get(card).equals(guess)) {
+          System.out.printf("Correct answer. ");
+        } else if (definitionToCard.containsKey(guess)) {
+          System.out.printf(
+              "Wrong answer (the correct one is \"%s\", you've just written a definition of \"%s\" card). ",
+              cardToDefinition.get(card), definitionToCard.get(guess));
+        } else {
+          System.out
+              .printf("Wrong answer (the correct one is \"%s\").", cardToDefinition.get(card));
+        }
+      }
     }
+  }
 }