Adding Simple Solution for Problem - 23 - Merge K Sorted Lists

Author: Vanditg

Merge_K_Sorted_List/EfficientSolution.py

@@ -0,0 +1,31 @@
+##==================================
+## Leetcode
+## Student: Vandit Jyotindra Gajjar
+## Year: 2020
+## Problem: 23
+## Problem Name: Merge k Sorted Lists  
+##===================================
+#
+#Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
+#
+#Example:
+#
+#Input:
+#[
+#  1->4->5,
+#  1->3->4,
+#  2->6
+#]
+#Output: 1->1->2->3->4->4->5->6
+class Solution:
+    def mergeKLists(self, lists):
+        tmp = []	#Initialize tmp empty list
+        dummy = head = ListNode(0)	#Initialize dummy linkedlist
+        for i in lists:	#Loop through lists
+            while i:	#Loop 
+                tmp.append(i.val)	#Append values in tmp list
+                i = i.next	#Traverse through list
+        for i in sorted(tmp):	#Loop through sorted tmp list
+            dummy.next = ListNode(i)	#Add the values in dummy linkedlist
+            dummy = dummy.next	#Point reference to next node 
+        return head.next	#Return our sorted dummy list

Merge_K_Sorted_List/SimpleSolution.py

@@ -19,13 +19,27 @@
 #Output: 1->1->2->3->4->4->5->6
 class Solution:
     def mergeKLists(self, lists):
-        tmp = []	#Initialize tmp empty list
-        dummy = head = ListNode(0)	#Initialize dummy linkedlist
-        for i in lists:	#Loop through lists
-            while i:	#Loop 
-                tmp.append(i.val)	#Append values in tmp list
-                i = i.next	#Traverse through list
-        for i in sorted(tmp):	#Loop through sorted tmp list
-            dummy.next = ListNode(i)	#Add the values in dummy linkedlist
-            dummy = dummy.next	#Point reference to next node 
-        return head.next	#Return our sorted dummy list
+        if not lists:	#Condition-check: If list is empty
+            return	#Return Empty 
+		if len(lists) == 1:	#Condition-check: If list has length of 1 
+            return lists[0]	#Return that element 
+        mid = len(lists) // 2	#Initialize mid point 
+        left = self.mergeKLists(lists[:mid])	#Initialize left by 0 to mid point 
+        right = self.mergeKLists(lists[mid:])	#Initialize right by mid point to last
+        return	self.merge(left, right)	#Return sorted list by using helper method 
+    def merge(self, list1, list2):	#Defining method merge that takes two list
+        tmp = dummy = ListNode(0)	#Initialize tmp and dummy which are empty linkedlist
+        while list1 and list2:	#Loop: List 1 and List 2 are not empty 
+            if list1.val <= list2.val:	#Condition-check: If list1.val is less than or equal to list2.val
+                tmp.next = ListNode(list1.val)	#Update the linkedlist by adding value of list1 
+                tmp = tmp.next	#Traverse through tmp 
+                list1 = list1.next	#Traverse through list1			 
+            else:	#Condition-check: Else
+                tmp.next = ListNode(list2.val)	#Update the linkedlist by adding value of list2
+                tmp = tmp.next	#Traverse through tmp 
+                list2 = list2.next	#Traverse through list2
+        if list1:	#Condition-check: If list1 is empty 
+            tmp.next = list1	#Change the point to list1
+        else:	#Condition-check: Else
+            tmp.next = list2	#Change the point to list2
+        return dummy.next	#Return the dummy linkedlist