Add quick sort algorithm in JavaScript (#909)

Author: tinniaru3005

Javascript/Algorithms/quick-sort.js

@@ -0,0 +1,42 @@
+var items = [5,3,7,6,2,9];
+function swap(items, leftIndex, rightIndex){
+    var temp = items[leftIndex];
+    items[leftIndex] = items[rightIndex];
+    items[rightIndex] = temp;
+}
+function partition(items, left, right) {
+    var pivot   = items[Math.floor((right + left) / 2)], //middle element
+        i       = left, //left pointer
+        j       = right; //right pointer
+    while (i <= j) {
+        while (items[i] < pivot) {
+            i++;
+        }
+        while (items[j] > pivot) {
+            j--;
+        }
+        if (i <= j) {
+            swap(items, i, j); //sawpping two elements
+            i++;
+            j--;
+        }
+    }
+    return i;
+}
+
+function quickSort(items, left, right) {
+    var index;
+    if (items.length > 1) {
+        index = partition(items, left, right); //index returned from partition
+        if (left < index - 1) { //more elements on the left side of the pivot
+            quickSort(items, left, index - 1);
+        }
+        if (index < right) { //more elements on the right side of the pivot
+            quickSort(items, index, right);
+        }
+    }
+    return items;
+}
+// first call to quick sort
+var sortedArray = quickSort(items, 0, items.length - 1);
+console.log(sortedArray); //prints [2,3,5,6,7,9]