Added quick sort

Author: FreeTymeKiyan

Other/QuickSort.java

@@ -0,0 +1,48 @@
+/**
+ * Quick sort an integer arrays
+ * 
+ * Tags: Sort
+ */
+class QuickSort {
+    public static void main(String[] args) {
+        QuickSort q = new QuickSort();
+        int[] A = { 1, 4, 2, 8, 5};
+        q.sort(A, 0, A.length - 1);
+        for (int n : A) System.out.print(n + ",");
+    }
+    
+    /**
+     * Partition the array according to middle index
+     * Sort left half, from left to index - 1
+     * Sort right half, from index to right
+     */
+    public void sort(int[] A, int left, int right) {
+        int index = partition(A, left, right);
+        if (left < index - 1) sort(A, left, index - 1);
+        if (index < right) sort(A, index, right);
+    }
+    
+    /**
+     * Choose pivot
+     * Init 2 pointers from both ends to do partition
+     * Move left pointer if A[left] is smaller than pivot(skip smaller)
+     * Move right pointer if A[right] is bigger than pivot(skip bigger)
+     * Check if left <= right, if so, swap left and right, move them
+     * Return left index
+     */
+    private int partition(int[] A, int left, int right) {
+        int pivot = A[left + (right - left) / 2];
+        while (left <= right) {
+            while (A[left] < pivot) left++;
+            while (A[right] > pivot) right--;
+            if (left <= right) {
+                int temp = A[left];
+                A[left] = A[right];
+                A[right] = temp;
+                left++;
+                right--;
+            }
+        }
+        return left;
+    }
+}