Fix the insertion sort (trekhleb#86)

* Fix LinkedList

* Fix the prepend method for the LinkedList

* Fix the remove method for the MinHeap

* Correct a comment

* Fix BST removal method

* Fix the findEdge method of the graph

* Fix the value returned by DisjointSet union

* Add recursive factorial function

* Fix the insertion sort

src/algorithms/sorting/insertion-sort/InsertionSort.js

@@ -14,7 +14,7 @@ export default class InsertionSort extends Sort {
       // Go and check if previous elements and greater then current one.
       // If this is the case then swap that elements.
       while (
-        array[currentIndex - 1] &&
+        array[currentIndex - 1] !== undefined &&
         this.comparator.lessThan(array[currentIndex], array[currentIndex - 1])
       ) {
         // Call visiting callback.