add merge linked lists algorithms

Author: Pl4tt

python/datastructures/merge_linked_lists.py

@@ -0,0 +1,66 @@
+from typing import Optional
+
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+    def __str__(self):
+        s = self
+        ret = []
+        while s:
+            ret.append(s.val)
+            s = s.next
+        return str(ret)
+
+
+def mergeTwoLists(l1: ListNode, l2: ListNode) -> ListNode:
+    if not l1:
+        return l2
+    if not l2:
+        return l1
+
+    if l1.val < l2.val:
+        result = l1.val
+        l1 = l1.next
+    else:
+        result = l2.val
+        l2 = l2.next
+        
+    return ListNode(result, mergeTwoLists(l1, l2))
+
+def mergeKLists(lists: list[Optional[ListNode]]) -> Optional[ListNode]:
+    nodes = []
+    result = curr = ListNode()
+    
+    for lst in lists:
+        while lst:
+            nodes.append(lst.val)
+            lst = lst.next
+    
+    for node in sorted(nodes):
+        curr.next = ListNode(node)
+        curr = curr.next
+        
+    return result.next
+
+
+if __name__ == "__main__":
+    # TESTS
+    l1 = ListNode(1, ListNode(4, ListNode(81)))
+    l2 = ListNode(1, ListNode(3, ListNode(4)))
+    l3 = ListNode(2, ListNode(3, ListNode(5)))
+    l4 = ListNode(2, ListNode(3, ListNode(5)))
+    l5 = ListNode(2, ListNode(26, ListNode(73)))
+    l6 = ListNode(2, ListNode(3, ListNode(62)))
+    l7 = ListNode(6, ListNode(10, ListNode(20)))
+    l8 = ListNode(2, ListNode(3, ListNode(51)))
+    l9 = ListNode(2, ListNode(3, ListNode(12)))
+    l10 = ListNode(3, ListNode(10, ListNode(20)))
+    l11 = ListNode(2, ListNode(3, ListNode(5)))
+    l12 = ListNode(2, ListNode(3, ListNode(66)))
+    l13 = ListNode(5, ListNode(6, ListNode(6)))
+    
+    print(mergeTwoLists(l1, l2))
+    print(mergeKLists([l1, l2, l3, l4, l5, l6, l7, l8, l9, l10, l11, l12, l13]))