Add new programs

Author: ShubhSingh

mypc/main/java/MergeSort.java

@@ -1,6 +1,9 @@
 package main.java;
 
-/* Java program for Merge Sort */
+/*
+* Rutime of merge sort: O(nlogn) average and worst case
+* Memory: O(n)
+* */
 class MergeSort
 {
     // Merges two subarrays of arr[].
@@ -80,7 +83,6 @@ void sort(int arr[], int l, int r)
         }
     }
 
-    /* A utility function to print array of size n */
     static void printArray(int arr[])
     {
         int n = arr.length;

mypc/main/java/QuickSort.java

@@ -0,0 +1,66 @@
+package main.java;
+
+/*
+ * Rutime of quicksort: O(nlogn) average, O(n2) worst case
+ * Memory: O(logn)
+ * */
+public class QuickSort {
+
+	public static void quicksort(int[] array) {
+		quicksort(array, 0, array.length-1);
+	}
+	
+	public static void quicksort(int[] array, int left, int right) {
+		if(left >= right) {
+			return;
+		}
+		int pivot = array[(left + right)/2]; // pick pivot point
+		int index = partition(array, left, right, pivot);
+		quicksort(array, left, index-1);
+		quicksort(array, index, right);
+			
+	}
+
+	public static int partition(int[] array, int left, int right, int pivot) {
+		while(left <= right) {
+			// find element on left that should be on right
+			while(array[left] < pivot) {
+				left++;
+			}
+			// find element on right that should be on left
+			while(array[right] > pivot) {
+				right--;
+			}
+			if(left <= right) {
+				swap(array, left, right);
+				left++;
+				right--;
+			}
+		}
+		return left;
+	}
+
+	public static void swap(int[] array, int left, int right) {
+		int tmp = array[left];
+		array[left] = array[right];
+		array[right] =  tmp;
+	}
+
+	static void printArray(int arr[])
+    {
+        int n = arr.length;
+        for (int i=0; i<n; ++i)
+            System.out.print(arr[i] + " ");
+        System.out.println();
+    }
+	
+	public static void main(String[] args) {
+		int[] arr = {7,22,18,25,10,5,6,2};
+		System.out.println("Before sorting array:");
+		printArray(arr);
+		quicksort(arr);
+		System.out.println("\nAfter sorting array:");
+		printArray(arr);
+	}
+
+}