Data commit

Task/Cheryls-birthday/Java/cheryls-birthday.java

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+import java.time.Month;
+import java.util.Collection;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+public class Main {
+    private static class Birthday {
+        private Month month;
+        private int day;
+
+        public Birthday(Month month, int day) {
+            this.month = month;
+            this.day = day;
+        }
+
+        public Month getMonth() {
+            return month;
+        }
+
+        public int getDay() {
+            return day;
+        }
+
+        @Override
+        public String toString() {
+            return month + " " + day;
+        }
+    }
+
+    public static void main(String[] args) {
+        List<Birthday> choices = List.of(
+            new Birthday(Month.MAY, 15),
+            new Birthday(Month.MAY, 16),
+            new Birthday(Month.MAY, 19),
+            new Birthday(Month.JUNE, 17),
+            new Birthday(Month.JUNE, 18),
+            new Birthday(Month.JULY, 14),
+            new Birthday(Month.JULY, 16),
+            new Birthday(Month.AUGUST, 14),
+            new Birthday(Month.AUGUST, 15),
+            new Birthday(Month.AUGUST, 17)
+        );
+        System.out.printf("There are %d candidates remaining.\n", choices.size());
+
+        // The month cannot have a unique day because Albert knows the month, and knows that Bernard does not know the answer
+        Set<Month> uniqueMonths = choices.stream()
+            .collect(Collectors.groupingBy(Birthday::getDay))
+            .values()
+            .stream()
+            .filter(g -> g.size() == 1)
+            .flatMap(Collection::stream)
+            .map(Birthday::getMonth)
+            .collect(Collectors.toSet());
+        List<Birthday> f1List = choices.stream()
+            .filter(birthday -> !uniqueMonths.contains(birthday.month))
+            .collect(Collectors.toList());
+        System.out.printf("There are %d candidates remaining.\n", f1List.size());
+
+        // Bernard now knows the answer, so the day must be unique within the remaining choices
+        List<Birthday> f2List = f1List.stream()
+            .collect(Collectors.groupingBy(Birthday::getDay))
+            .values()
+            .stream()
+            .filter(g -> g.size() == 1)
+            .flatMap(Collection::stream)
+            .collect(Collectors.toList());
+        System.out.printf("There are %d candidates remaining.\n", f2List.size());
+
+        // Albert knows the answer too, so the month must be unique within the remaining choices
+        List<Birthday> f3List = f2List.stream()
+            .collect(Collectors.groupingBy(Birthday::getMonth))
+            .values()
+            .stream()
+            .filter(g -> g.size() == 1)
+            .flatMap(Collection::stream)
+            .collect(Collectors.toList());
+        System.out.printf("There are %d candidates remaining.\n", f3List.size());
+
+        if (f3List.size() == 1) {
+            System.out.printf("Cheryl's birthday is %s\n", f3List.get(0));
+        } else {
+            System.out.println("No unique choice found");
+        }
+    }
+}