Create QuickSort.java

algorithms/QuickSort.java

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+public class QuickSort
+{
+  public static void main(String[] args) 
+  {
+    // This is unsorted array
+    Integer[] array = new Integer[] { 12, 13, 24, 10, 3, 6, 90, 70 };
+
+    // Let's sort using quick sort
+    quickSort( array, 0, array.length - 1 );
+
+    // Verify sorted array
+    System.out.println(Arrays.toString(array));
+  }
+
+  public static void quickSort(Integer[] arr, int low, int high) 
+  {
+    //check for empty or null array
+    if (arr == null || arr.length == 0){
+      return;
+    }
+
+    if (low >= high){
+      return;
+    }
+
+    //Get the pivot element from the middle of the list
+    int middle = low + (high - low) / 2;
+    int pivot = arr[middle];
+
+    // make left < pivot and right > pivot
+    int i = low, j = high;
+    while (i <= j) 
+    {
+      //Check until all values on left side array are lower than pivot
+      while (arr[i] < pivot) 
+      {
+        i++;
+      }
+      //Check until all values on left side array are greater than pivot
+      while (arr[j] > pivot) 
+      {
+        j--;
+      }
+      //Now compare values from both side of lists to see if they need swapping 
+      //After swapping move the iterator on both lists
+      if (i <= j) 
+      {
+        swap (arr, i, j);
+        i++;
+        j--;
+      }
+    }
+    //Do same operation as above recursively to sort two sub arrays
+    if (low < j){
+      quickSort(arr, low, j);
+    }
+    if (high > i){
+      quickSort(arr, i, high);
+    }
+  }
+
+  public static void swap (Integer array[], int x, int y)
+    {
+    int temp = array[x];
+    array[x] = array[y];
+    array[y] = temp;
+    }
+}