Merge pull request #12 from the-cybersapien/master

Add QuickSortRandomPivot.java

Sorting Algorithms/Quick Sort Algorithm/Java/QuickSortRandomPivot.java

@@ -0,0 +1,92 @@
+/* ===== ===== =====
+
+Theory of Programming
+
+Quick sort algorithm with random pivot selection
+http://theoryofprogramming.com/2015/01/20/quick-sort-algorithm/
+GitHub - https://github.com/VamsiSangam/theoryofprogramming
+Code Contributor - Aditya Aggarwal (github.com/the-cybersapien, cybersapien.xyz)
+
+===== ===== ===== */
+
+import java.util.Scanner;
+
+public class QuickSortRandomPivot {
+
+    public static void main(String[] args) {
+        // Initialize the Scanner Object to take input
+        Scanner in = new Scanner(System.in);
+        // Get the Size of the Array
+        System.out.println("Enter the size of the array:");
+        int size = in.nextInt();
+        // Initialize the Array for sorting the elements
+        int[] array = new int[size];
+        // Get the data from user
+        System.out.println("Enter the elements of the array: ");
+
+        for (int i = 0; i < size; i++) {
+            array[i] = in.nextInt();
+        }
+
+        // Call the quickSort function to sort the Array
+        quickSortRandomPivot(array, 0, size - 1);
+
+        // Print the Sorted Array
+        System.out.println("Sorted Array: ");
+
+        for (int a : array) {
+            System.out.print(a + " ");
+        }
+
+        System.out.println();
+    }
+
+    private static void quickSortRandomPivot(int[] array, int low, int high){
+        if (low >= high) {
+            // A single element is
+            // considered to be sorted
+            return;
+        }
+
+        // Choose a random pivot using the random number generator
+        // Additional brackets added here to ensure that there is no problems
+        // while typecasting from double to int due to precedence
+        int mid = (((int) (Math.random() * (high - low))) + low);
+
+        // Put the pivot at the last
+        int temp = array[mid];
+        array[mid] = array[high];
+        array[high] = temp;
+
+        int pivot = array[high];
+        int i = low;
+        int j = high - 1;
+
+        while (j >= i){
+            if (array[j] < pivot && array[i] > pivot){
+                temp = array[i];
+                array[i] = array[j];
+                array[j] = temp;
+
+                i++;
+                j--;
+            } else if (array[j] < pivot && array[i] <= pivot){
+                i++;
+            } else if (array[j] >= pivot && array[i] > pivot){
+                j--;
+            } else if (array[j] >= pivot && array[i] <= pivot){
+                i++;
+                j--;
+            }
+        }
+
+        // Bring the pivot back to its
+        // appropriate place
+        temp = array[i];
+        array[i] = array[high];
+        array[high] = temp;
+
+        quickSortRandomPivot(array, low, i - 1);
+        quickSortRandomPivot(array, i + 1, high);
+    }
+}