refactor reverse

Author: cicirello

src/main/java/org/cicirello/permutations/Permutation.java

@@ -760,9 +760,7 @@ public void swapBlocks(int a, int b, int i, int j) {
 
   /** Reverses the order of the elements in the permutation. */
   public void reverse() {
-    for (int i = 0, j = permutation.length - 1; i < j; i++, j--) {
-      internalSwap(i, j);
-    }
+    internalReverse(0, permutation.length - 1);
     hashCodeIsCached = false;
   }
 
@@ -776,13 +774,9 @@ public void reverse() {
    */
   public void reverse(int i, int j) {
     if (i > j) {
-      for (; i > j; i--, j++) {
-        internalSwap(i, j);
-      }
+      internalReverse(j, i);
     } else {
-      for (; i < j; i++, j--) {
-        internalSwap(i, j);
-      }
+      internalReverse(i, j);
     }
     hashCodeIsCached = false;
   }
@@ -959,6 +953,12 @@ private boolean validate(int[] p) {
     return true;
   }
 
+  private void internalReverse(int i, int j) {
+    for (; i < j; i++, j--) {
+      internalSwap(i, j);
+    }
+  }
+
   /*
    * Use internally, such as from reverse, etc to avoid
    * repeatedly invalidating hashCode cache (as well as from