chore(JavaScript): quick sort added (#270)

algorithms/JavaScript/README.md

@@ -14,8 +14,9 @@
 ## Sorting
 1. [Bubble Sort](src/sorting/bubble-sort.js)
 2. [Insertion Sort](src/sorting/insertion-sort.js)
-3. [Selection Sort](src/sorting/selection-sort.js)
+3. [Merge Sort](src/sorting/merge-sort.js)
-4. [Merge Sort](src/sorting/merge-sort.js)
+4. [Quick Sort](src/sorting/quick-sort.js)
+5. [Selection Sort](src/sorting/selection-sort.js)
  
 ## Strings
 1. [Palindrome](src/strings/palindrome.js)

algorithms/JavaScript/src/index.js

@@ -12,6 +12,8 @@ require('./searching/linear-search');
 // Sorting
 require('./sorting/bubble-sort');
 require('./sorting/insertion-sort');
+require('./sorting/merge-sort');
+require('./sorting/quick-sort');
 require('./sorting/selection-sort');
 
 // Strings

algorithms/JavaScript/src/sorting/quick-sort.js

@@ -0,0 +1,46 @@
+function swap(items, leftIndex, rightIndex) {
+  const temp = items[leftIndex];
+  items[leftIndex] = items[rightIndex];
+  items[rightIndex] = temp;
+}
+
+function partition(items, left, right) {
+  const pivot = items[Math.floor((right + left) / 2)]; // middle element
+  let i = left; // left pointer
+  let 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) {
+  let 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
+const items = [5, 3, 7, 6, 2, 9];
+const sortedArray = quickSort(items, 0, items.length - 1);
+console.log(sortedArray); // prints [2,3,5,6,7,9]