Initial data commit

Task/Pancake-numbers/Java/pancake-numbers-2.java

@@ -0,0 +1,47 @@
+import static java.util.Comparator.comparing;
+import static java.util.stream.Collectors.toList;
+
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Queue;
+import java.util.stream.IntStream;
+
+
+public class Pancake {
+
+    private static List<Integer> flipStack(List<Integer> stack, int spatula) {
+        List<Integer> copy = new ArrayList<>(stack);
+        Collections.reverse(copy.subList(0, spatula));
+        return copy;
+    }
+
+    private static Map.Entry<List<Integer>, Integer> pancake(int n) {
+        List<Integer> initialStack = IntStream.rangeClosed(1, n).boxed().collect(toList());
+        Map<List<Integer>, Integer> stackFlips = new HashMap<>();
+        stackFlips.put(initialStack, 1);
+        Queue<List<Integer>> queue = new ArrayDeque<>();
+        queue.add(initialStack);
+        while (!queue.isEmpty()) {
+            List<Integer> stack = queue.remove();
+            int flips = stackFlips.get(stack) + 1;
+            for (int i = 2; i <= n; ++i) {
+                List<Integer> flipped = flipStack(stack, i);
+                if (stackFlips.putIfAbsent(flipped, flips) == null) {
+                    queue.add(flipped);
+                }
+            }
+        }
+        return stackFlips.entrySet().stream().max(comparing(e -> e.getValue())).get();
+    }
+
+    public static void main(String[] args) {
+        for (int i = 1; i <= 10; ++i) {
+            Map.Entry<List<Integer>, Integer> result = pancake(i);
+            System.out.printf("pancake(%s) = %s. Example: %s\n", i, result.getValue(), result.getKey());
+        }
+    }
+}