1 files changed, 47 insertions, 0 deletions

diff --git a/src/ch/epfl/xblast/Lists.java b/src/ch/epfl/xblast/Lists.java
new file mode 100644
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+++ b/src/ch/epfl/xblast/Lists.java
@@ -0,0 +1,47 @@
+package ch.epfl.xblast;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * Lists utility class providing common operations on lists.
+ *
+ * @author Pacien TRAN-GIRARD (261948)
+ * @author Timothée FLOURE (257420)
+ */
+public final class Lists {
+
+    /**
+     * Returns a reversed copy of the given list, leaving the original one unmodified.
+     *
+     * @param l   the list to reverse
+     * @param <T> the type of the list's elements
+     * @return a reversed copy of the list.
+     */
+    public static <T> List<T> reversed(List<T> l) {
+        List<T> r = new ArrayList<>(l);
+        Collections.reverse(r);
+        return r;
+    }
+
+    /**
+     * Returns a symmetric version of the list, without repeating the last element of the input list.
+     * For instance, mirrored([kay]) will return [kayak].
+     *
+     * @param l   the input list
+     * @param <T> the type of the list's elements
+     * @return the mirrored list
+     * @throws IllegalArgumentException if the given list is empty
+     */
+    public static <T> List<T> mirrored(List<T> l) {
+        if (l == null || l.size() == 0) throw new IllegalArgumentException();
+
+        return Stream
+                .concat(l.stream(), Lists.reversed(l).stream().skip(1))
+                .collect(Collectors.toList());
+    }
+
+}