Merge pull request TheAlgorithms#786 from CN-GuoZiyang/master

yanglbme · web-flow · commit 2bf163d6a189 · 2019-07-06T21:44:28.000+08:00
Using randomize partition to avoid the basically ordered sequences
diff --git a/Sorts/QuickSort.java b/Sorts/QuickSort.java
@@ -33,12 +33,27 @@ public <T extends Comparable<T>> T[] sort(T[] array) {
 
     private static <T extends Comparable<T>> void doSort(T[] array, int left, int right) {
         if (left < right) {
-            int pivot = partition(array, left, right);
+            int pivot = randomPartition(array, left, right);
             doSort(array, left, pivot - 1);
             doSort(array, pivot, right);
         }
     }
 
+    /**
+     * Ramdomize the array to avoid the basically ordered sequences
+     * 
+     * @param array The array to be sorted
+     * @param left  The first index of an array
+     * @param right The last index of an array
+     * @return the partition index of the array
+     */
+
+    private static <T extends Comparable<T>> int randomPartition(T[] array, int left, int right) {
+        int randomIndex = left + (int)(Math.random()*(right - left + 1));
+        swap(array, randomIndex, right);
+        return partition(array, left, right);
+    }
+
     /**
      * This method finds the partition index for an array
      *
@@ -75,7 +90,7 @@ public static void main(String[] args) {
         Integer[] array = {3, 4, 1, 32, 0, 1, 5, 12, 2, 5, 7, 8, 9, 2, 44, 111, 5};
 
         QuickSort quickSort = new QuickSort();
-        // quickSort.sort(array);
+        quickSort.sort(array);
 
         //Output => 0 1 1 2 2 3 4 5 5 5 7 8 9 12 32 44 111
         print(array);
