added Java QuickSort

Sorting Algorithms/Java/QuickSort.java

@@ -0,0 +1,46 @@
+import java.util.Arrays;
+
+public class QuickSort {
+    public static void main(String[] args) {
+        int[] arr = {5,75,3,65,2,1,3,4,4,88};
+        System.out.println(Arrays.toString(arr));
+        quickSort(arr, 0, arr.length-1);
+        System.out.println(Arrays.toString(arr));
+    }
+
+    public static void quickSort(int[] arr, int leftStart, int rightEnd){
+        if(leftStart < rightEnd){
+            int partition = partition(arr, leftStart, rightEnd);
+            quickSort(arr, leftStart, partition - 1);
+            quickSort(arr, partition+1, rightEnd);
+        }
+    }
+
+    public static int partition(int[] arr, int low, int high){
+
+        // improved performance when the array is already sorted
+        int mid = low + (high - low) / 2;
+        swap(arr, mid, high);
+
+        // choosing the high as the pivot
+        int pivot = arr[high];
+        int i = low - 1;
+
+        for (int j = low; j < high; j++){
+            if(arr[j] <= pivot){
+                i++;
+                swap(arr, j, i);
+            }
+        }
+
+        swap(arr, high, i+1);
+
+        return i+1;
+    }
+
+    public static void swap(int[] arr, int a, int b) {
+        int temp = arr[a];
+        arr[a] = arr[b];
+        arr[b] = temp;
+    }
+}