Merge pull request #472 from Tech-neophyte/patch-5

day 22-q3 (py3, cpp) solution added #440

Day-22/q3: Sort List/Tech-neophyte--cp.md

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+## Cpp code: merge sort
+```
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    /// Merge Function
+
+    ListNode *mergeList(ListNode *l1, ListNode *l2){
+        ListNode *prev=new ListNode(-1), *curr=prev;
+        while(l1 and l2){
+            if(l1->val<=l2->val){
+                curr->next=l1;
+                l1=l1->next;
+            }else{
+                curr->next=l2;
+                l2=l2->next;
+            }
+        curr=curr->next;
+        }
+        if(l1){
+            curr->next=l1;
+            l1=l1->next;
+        }
+        if(l2){
+            curr->next=l2;
+            l2=l2->next;
+        }
+    return prev->next;
+    }
+
+    /// Divide and Conquer Approach (Merge Sort)
+
+    ListNode* sortList(ListNode* head){
+        if(!head or !head->next) return head;
+        ListNode *slow=head, *fast=head, *temp=NULL;
+        while(fast and fast->next){
+            temp=slow;
+            slow=slow->next;
+            fast=fast->next->next;
+        }
+        temp->next=NULL;
+
+        ListNode *point1=sortList(head), *point2=sortList(slow);
+    return mergeList(point1,point2);        
+    }
+};
+```
+## Python code: (Using lists)
+```
+class Solution:
+    def sortList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        curr = head
+        l =[]
+        while curr:
+            l.append(curr.val)
+            curr = curr.next
+        l.sort()
+        curr = head
+        for i in l:
+            curr.val = i
+            curr = curr.next
+        return head
+```