merge: Bubble Sort enhancements for nearly sorted or sorted array, added test cases and documentation (TheAlgorithms#895)

* BubbleSort enacements for nearly sorted or sorted array and added test cases

* BubbleSort enacements for nearly sorted or sorted array and added test cases

* Bubble sort requested changes solved

* standard js style issue fixed

Author: aminhossain

Sorts/BubbleSort.js

@@ -2,6 +2,7 @@
 *  compares adjacent element and swaps their position
 *  The big O on bubble sort in worst and best case is O(N^2).
 *  Not efficient.
+*  Somehow if the array is sorted or nearly sorted then we can optimize bubble sort by adding a flag.
 *
 *  In bubble sort, we keep iterating while something was swapped in
 *  the previous inner-loop iteration. By swapped I mean, in the
@@ -17,16 +18,23 @@
  */
 export function bubbleSort (items) {
   const length = items.length
+  let noSwaps
 
-  for (let i = (length - 1); i > 0; i--) {
+  for (let i = length; i > 0; i--) {
+    // flag for optimization
+    noSwaps = true
     // Number of passes
-    for (let j = (length - i); j > 0; j--) {
+    for (let j = 0; j < (i - 1); j++) {
       // Compare the adjacent positions
-      if (items[j] < items[j - 1]) {
+      if (items[j] > items[j + 1]) {
         // Swap the numbers
-        [items[j], items[j - 1]] = [items[j - 1], items[j]]
+        [items[j], items[j + 1]] = [items[j + 1], items[j]]
+        noSwaps = false
       }
     }
+    if (noSwaps) {
+      break
+    }
   }
 
   return items

Sorts/test/BubbleSort.test.js

@@ -6,6 +6,7 @@ describe('bubbleSort', () => {
     expect(bubbleSort([])).toEqual([])
     expect(bubbleSort([1, 2, 3])).toEqual([1, 2, 3])
     expect(bubbleSort([5, 6, 7, 8, 1, 2, 12, 14])).toEqual([1, 2, 5, 6, 7, 8, 12, 14])
+    expect(bubbleSort([5, 6, 7, 8, 9, 4])).toEqual([4, 5, 6, 7, 8, 9])
   })
 })