add rotate

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/src/algorithms/arrays/Rotate.java b/src/algorithms/arrays/Rotate.java
new file mode 100644
index 0000000..22ba033
--- /dev/null
+++ b/src/algorithms/arrays/Rotate.java
@@ -0,0 +1,66 @@
+/**
+ * Copyright © 2014  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package algorithms.arrays;
+
+import java.util.*;
+
+
+/**
+ * Class for rotating arrays
+ */
+public class Rotate
+{
+    /*
+     *  There are many thing you can change in this class to adapt it, for example,
+     *  if you want in-place rotation, which probabily is a bit slower (even though
+     *  it is less naïve), you can reverse the array, split it at the index 'steps',
+     *  and reverse those partitions and the concatinate back again, of cause, you
+     *  would only reverse parts of the array, not split and concatinate it.
+     *  You could also reverse the array while rotating it, either reverse the
+     *  input or the output.
+     */
+    
+    
+£<for T in boolean char byte short int long float double T; do
+  P= O="$T" cast=
+£>[ $T = T ] && P="<T> " O=Object cast="(T[])"
+    /**
+     * Rotates an array
+     *
+     * @param   items  The array to rotate
+     * @param   steps  The number of steps to higher index to rotate elements
+     * @return         The array rotated
+     */
+£>[ $T = T ] &&
+    @SuppressWarnings("unchecked")
+    public static £{P}£{T}[] rotateClone(£{T}[] items, int steps)
+    {
+	£{O}[] rc = new £{O}[items.length];
+	
+	int n = items.length;
+	if ((n & -n) == n) /* power of 2 */
+	    for (int i = 0, m = n - 1; i < n; i++)
+		rc[(steps + i) & m] = items[i];
+	else
+	    for (int i = 0; i < n; i++)
+		rc[(steps + i) % n] = items[i];
+	
+	return £{cast}rc;
+    }
+£>done
+}
+