Create Reverse_Nodes_in_K_group.py

Author: Ram-95

Linked_Lists/Reverse_Nodes_in_K_group.py

@@ -0,0 +1,35 @@
+"""
+Use a dummy head, and
+
+l, r : define reversing range
+
+pre, cur : used in reversing, standard reverse linked linked list method
+
+jump : used to connect last node in previous k-group to first node in following k-group
+"""
+class Solution:
+    def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
+        # Dummy node initialization
+        dummy = jump = ListNode(-1)
+        dummy.next = l = r = head
+        
+        while True:
+            count = 0
+            # Moving k positions
+            while r and count < k:
+                count += 1
+                r = r.next
+            # If count == k, then reverse the segment [l, r]
+            if count == k:
+                pre, cur = r, l
+                for _ in range(k):
+                    temp = cur.next
+                    cur.next = pre
+                    pre = cur
+                    cur = temp
+                # Joining the current k-group with the previous k-group
+                jump.next = pre
+                jump = l
+                l = r
+            else:
+                return dummy.next