refactored some recursive content including tests

and deleted question that is from test and not
related to interview question, also its complicated to understand its description

code-questions/recursive/__tests__/merge-sort.test.js

@@ -6,14 +6,14 @@ describe('merge-sort tests', () => {
             [1, 3, 4, 5, 6, 7, -9, 0, 2],
             [-9, 0, 1, 2, 3, 4, 5, 6, 7],
         ],
-        [
-            [41, 3, 5, 6, 7, -9, 0, 2],
-            [-9, 0, 2, 3, 5, 6, 7, 41],
-        ],
         [
             [-1, -9, -88, 0, -4, 2],
             [-88, -9, -4, -1, 0, 2],
         ],
+        [
+            [3, 2, 1, 0],
+            [0, 1, 2, 3],
+        ],
         [
             [1, 2, 3],
             [1, 2, 3],
@@ -22,10 +22,6 @@ describe('merge-sort tests', () => {
             [32, -7],
             [-7, 32],
         ],
-        [
-            [3, 2, 1, 0],
-            [0, 1, 2, 3],
-        ],
         [[1], [1]],
         [[], []],
     ])('function accepts arr: %s, then return result: %s', (arr, res) => {

code-questions/recursive/merge-sort.js

@@ -1,4 +1,30 @@
-// Implement merge sort
+/* Given an array arr[], its starting position l and its ending position r. 
+Sort the array using merge sort algorithm.
+
+Example 1:
+    Input:
+        N = 5
+        arr[] = {4 1 3 9 7}
+    Output:
+        1 3 4 7 9
+
+Example 2:
+    Input:
+        N = 10
+        arr[] = {10 9 8 7 6 5 4 3 2 1}
+    Output:
+        1 2 3 4 5 6 7 8 9 10
+
+Your Task:
+    You don't need to take the input or print anything. 
+    Your task is to complete the function merge() which takes 
+    arr[], l, m, r as its input parameters and modifies arr[] in-place 
+    such that it is sorted from position l to position r, 
+    and function mergeSort() which uses merge() to sort the array 
+    in ascending order using merge sort algorithm.
+
+Expected Time Complexity: O(NLogN) 
+Expected Auxiliary Space: O(N) */
 
 module.exports.mergeSort = function (initialArray) {
     return initialArray.length ? halving(initialArray) : initialArray;
@@ -22,7 +48,6 @@ module.exports.mergeSort = function (initialArray) {
                 case arr1[0] <= arr2[0]:
                     sortedArray.push(arr1.shift(0, 1));
                     break;
-
                 case arr1.length === 0:
                 case arr2[0] < arr1[0]:
                     sortedArray.push(arr2.shift(0, 1));

code-questions/recursive/merge-two-sorted-lists.js

@@ -1,37 +1,35 @@
-/* Given two sorted linked lists consisting of N and M nodes 
-respectively. The task is to merge both of the list (in-place) 
+/* Given two sorted linked lists consisting of N and M nodes respectively. 
+The task is to merge both of the list (in-place) 
 and return head of the merged list. 
 
 Example 1:
-
-Input:
-N = 4, M = 3 
-valueN[] = {5,10,15,40}
-valueM[] = {2,3,20}
-
-Output: 2 3 5 10 15 20 40
-
-Explanation: After merging the two linked
-lists, we have merged list as 2, 3, 5,
-10, 15, 20, 40.
+    Input:
+        N = 4
+        M = 3 
+        valueN[] = {5,10,15,40}
+        valueM[] = {2,3,20}
+    Output: 
+        2 3 5 10 15 20 40
+    Explanation: 
+        After merging the two linked lists, 
+        we have merged list as 2, 3, 5, 10, 15, 20, 40.
 
 Example 2:
-
-Input:
-N = 2, M = 2
-valueN[] = {1,1}
-valueM[] = {2,4}
-
-Output: 1 1 2 4
-
-Explanation: After merging the given two
-linked list , we have 1, 1, 2, 4 as
-output.
+    Input:
+        N = 2 
+        M = 2
+        valueN[] = {1,1}
+        valueM[] = {2,4}
+    Output: 
+        1 1 2 4
+    Explanation: 
+        After merging the given two linked list, 
+        we have 1, 1, 2, 4 as output.
 
 Your Task:
-The task is to complete the function sortedMerge() 
-which takes references to the heads of two linked lists 
-as the arguments and returns the head of merged linked list.
+    The task is to complete the function sortedMerge() 
+    which takes references to the heads of two linked lists 
+    as the arguments and returns the head of merged linked list.
 
 Expected Time Complexity : O(n+m)
 Expected Auxilliary Space : O(1) */
@@ -47,28 +45,28 @@ module.exports.sortedMerge = function (head1, head2) {
     return head1.value < head2.value ? head1 : head2;
 
     function rec(node1, node2) {
-        if (node1.next === null) {
-            if (node2 !== null) node1.next = node2;
-            return;
-        }
-
-        if (node1.value <= node2.value) {
-            prev1 = node1;
-            rec(node1.next, node2);
-        } else {
-            if (!prev1) {
+        switch (true) {
+            case node1.next === null:
+                node1.next = node2 || node1.next;
+                return;
+            case node1.value <= node2.value:
                 prev1 = node1;
-                node1 = node1.next;
-                prev2 = node2;
-                node2 = node2.next;
-                prev2.next = prev1;
-            } else {
-                prev2 = node2;
-                node2 = node2.next;
-                prev1.next = prev2;
-                prev2.next = node1;
-            }
-            rec(node1, node2);
+                rec(node1.next, node2);
+                break;
+            default:
+                if (!prev1) {
+                    prev1 = node1;
+                    node1 = node1.next;
+                    prev2 = node2;
+                    node2 = node2.next;
+                    prev2.next = prev1;
+                } else {
+                    prev2 = node2;
+                    node2 = node2.next;
+                    prev1.next = prev2;
+                    prev2.next = node1;
+                }
+                rec(node1, node2);
         }
     }
 };