iluwatar#1 Add quicksort snippet

iluwatar · iluwatar · commit 170eda008310 · 2018-01-07T19:44:23.000+02:00
diff --git a/README.md b/README.md
@@ -9,6 +9,9 @@ Update the sample application with the snippet and add a test for it. After prov
 
 ## Table of Contents
 
+### Algorithm
+* [Quicksort](#quicksort)
+
 ### Array
 * [Generic two array concatenation](#generic-two-array-concatenation)
 * [Generic N array concatenation](#generic-N-array-concatenation)
@@ -33,6 +36,41 @@ Update the sample application with the snippet and add a test for it. After prov
 * [Reverse string](#reverse-string)
 * [String to date](#string-to-date)
 
+## Algorithm
+
+### Quicksort
+
+```java
+    public static void quickSort(int[] arr, int left, int right) {
+        int pivotIndex = left + (right - left) / 2;
+        int pivotValue = arr[pivotIndex];
+        int i = left, j = right;
+        while (i <= j) {
+            while (arr[i] < pivotValue) {
+                i++;
+            }
+            while (arr[j] > pivotValue) {
+                j--;
+            }
+            if (i <= j) {
+                int tmp = arr[i];
+                arr[i] = arr[j];
+                arr[j] = tmp;
+                i++;
+                j--;
+            }
+            if (left < i) {
+                quickSort(arr, left, j);
+            }
+            if (right > i) {
+                quickSort(arr, i, right);
+            }
+        }
+    }
+```
+
+[⬆ back to top](#table-of-contents)
+
 ## Array
 
 ### Generic two array concatenation
diff --git a/src/main/java/Library.java b/src/main/java/Library.java
@@ -216,4 +216,37 @@ public static void zipFile(String srcFilename, String zipFilename) throws IOExce
             }
         }
     }
+
+    /**
+     * Sort an array with quicksort algorithm
+     * @param arr array to sort
+     * @param left left index where to begin sort (e.g. 0)
+     * @param right right index where to end sort (e.g. array length - 1)
+     */
+    public static void quickSort(int[] arr, int left, int right) {
+        int pivotIndex = left + (right - left) / 2;
+        int pivotValue = arr[pivotIndex];
+        int i = left, j = right;
+        while (i <= j) {
+            while (arr[i] < pivotValue) {
+                i++;
+            }
+            while (arr[j] > pivotValue) {
+                j--;
+            }
+            if (i <= j) {
+                int tmp = arr[i];
+                arr[i] = arr[j];
+                arr[j] = tmp;
+                i++;
+                j--;
+            }
+            if (left < i) {
+                quickSort(arr, left, j);
+            }
+            if (right > i) {
+                quickSort(arr, i, right);
+            }
+        }
+    }
 }
diff --git a/src/test/java/LibraryTest.java b/src/test/java/LibraryTest.java
@@ -212,4 +212,20 @@ public void testZipFile() throws IOException {
             Files.deleteIfExists(new File(dst).toPath());
         }
     }
+
+    /**
+     * Tests for {@link Library#quickSort(int[], int, int)}
+     */
+    @Test
+    public void testQuickSort() {
+        int[] arr = new int[] {7, 13, 3, 1, 8, 5};
+        Library.quickSort(arr, 0, arr.length - 1);
+        assertEquals(arr.length, 6);
+        assertEquals(arr[0], 1);
+        assertEquals(arr[1], 3);
+        assertEquals(arr[2], 5);
+        assertEquals(arr[3], 7);
+        assertEquals(arr[4], 8);
+        assertEquals(arr[5], 13);
+    }
 }
