- Merge Two Sorted Lists #224

Author: ayosecu

merge-two-sorted-lists/ayosecu.py

@@ -0,0 +1,62 @@
+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:
+    """
+        - Time Complexity: O(n + m), n = len(list1), m = len(list2)
+        - Space Complexity: O(1)
+    """
+    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
+        # two pointers
+        p1, p2 = list1, list2
+        dummy = ListNode(0)
+        current = dummy
+        
+        while p1 and p2:  
+            if p1.val < p2.val:
+                current.next = p1
+                p1 = p1.next
+            else:
+                current.next = p2
+                p2 = p2.next
+            current = current.next
+        
+        current.next = p1 if p1 else p2
+        
+        return dummy.next
+
+def printList(list):
+    if not list:
+        print("[]")
+        return
+    
+    str_list = []
+    while list:
+        str_list.append(str(list.val))
+        list = list.next
+    print("[" + ", ".join(str_list) + "]")
+
+def doTest():
+    sol = Solution()
+
+    list1 = ListNode(1)
+    list1.next = ListNode(2)
+    list1.next.next = ListNode(4)
+    list2 = ListNode(1)
+    list2.next = ListNode(3)
+    list2.next.next = ListNode(4)
+    result1 = sol.mergeTwoLists(list1, list2)
+    printList(result1)
+
+    result2 = sol.mergeTwoLists(None, None)
+    printList(result2)
+
+    result3 = sol.mergeTwoLists(None, ListNode(0))
+    printList(result3)
+
+doTest()