rotate + reverse

Author: make-github-pseudonymous-again

js/dist/array.js

@@ -919,6 +919,35 @@ var repr = function ( array, left, right ) {
 
 exports.repr = repr;
 
+/* js/src/reverse.js */
+
+var reverse = function ( a , i , j ) {
+
+	while ( i < j ) swap( a , i++ , --j ) ;
+
+} ;
+
+exports.reverse = reverse ;
+
+/* js/src/rotate.js */
+
+/**
+ * In place O(n).
+ *
+ * Rotate right version.
+ * See http://prakhar.me/articles/the-string-rotation-problem/.
+ */
+
+var rotate = function ( a , i , j , n ) {
+
+	reverse( a , i , j ) ;
+	reverse( a , i , i + n ) ;
+	reverse( a , i + n , j ) ;
+
+} ;
+
+exports.rotate = rotate ;
+
 /* js/src/set.js */
 
 var set = function ( a , i , v ) {

js/dist/array.js.map

@@ -0,0 +1,8 @@
+
+var reverse = function ( a , i , j ) {
+
+	while ( i < j ) swap( a , i++ , --j ) ;
+
+} ;
+
+exports.reverse = reverse ;

js/dist/array.min.js

@@ -0,0 +1,17 @@
+
+/**
+ * In place O(n).
+ *
+ * Rotate right version.
+ * See http://prakhar.me/articles/the-string-rotation-problem/.
+ */
+
+var rotate = function ( a , i , j , n ) {
+
+	reverse( a , i , j ) ;
+	reverse( a , i , i + n ) ;
+	reverse( a , i + n , j ) ;
+
+} ;
+
+exports.rotate = rotate ;

js/src/reverse.js

@@ -0,0 +1,25 @@
+
+test( "rotate" , function ( ) {
+
+
+	var a , b , n ;
+
+	n = 1000 ;
+
+	a = array.alloc( n ) ;
+
+	b = array.alloc( n ) ;
+
+	array.iota( a , 0 , n , 0 ) ;
+
+	array.copy( a , 0 , n , b , 0 ) ;
+
+	array.rotate( a , 0 , n , n - 3 ) ;
+
+	b = b.concat( b.splice( 0 , 3 ) ) ;
+
+	deepEqual( a.length , n , "length did not change" ) ;
+
+	deepEqual( a , b , "works as expected" ) ;
+
+} ) ;