merge sorted lists

source LeetCode

Author: SanjarH

merge_linked_list.py

@@ -0,0 +1,57 @@
+# Learn Python together
+"""You are given the heads of two sorted linked lists list1 and list2.
+Merge the two lists in a one sorted list. The list should be made by
+splicing together the nodes of the first two lists.
+Return the head of the merged linked list."""
+
+# Solution
+# import Optional type
+from typing import Optional
+
+#Definition for singly-linked list.
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+class Solution:
+    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]):
+         
+        if not list1 or not list2: # If one of the lists is empty,
+            return list1 or list2  # return the other list 
+        # comparing lists values for getting lower value
+        if list1.val < list2.val:
+            # lover value from list1
+            head = list1
+            # using recursive get other values in tail variable
+            tail = self.mergeTwoLists(list1.next, list2)
+        else: # if the value of second node is lower than first node
+            # lover value from list2
+            head = list2
+            # using recursive get other values in tail variable
+            tail = self.mergeTwoLists(list1, list2.next)
+        #  connects the head node and the tail node of the merged linked list
+        head.next = tail
+        return head # return current node
+
+#check    
+list1 = ListNode(1, ListNode(2, ListNode(4)))
+list2 = ListNode(1, ListNode(3, ListNode(4)))
+solution = Solution()
+result = solution.mergeTwoLists(list1, list2)
+expected_result = ListNode(1, ListNode(1, ListNode(2, ListNode(3, ListNode(4, ListNode(4))))))
+
+# funtion to printing linked-list result
+def print_list(head):
+    node = head
+    while node:
+        # print current value and '->' if there is a next value in linked-list else empty string
+        print(node.val, end=" -> " if node.next else "")
+        # moving to next value
+        node = node.next 
+    print()
+
+print_list(result) 
+# Output -> 1 -> 1 -> 2 -> 3 -> 4 -> 4
+print_list(expected_result)
+# Output -> 1 -> 1 -> 2 -> 3 -> 4 -> 4
+