From 6bc1bcb772f53e7feb351d62a63b33ac94cee147 Mon Sep 17 00:00:00 2001
From: Deven <63876261+devenperez@users.noreply.github.com>
Date: Mon, 8 Dec 2025 18:17:52 -0500
Subject: [PATCH] Time: 4 ms (13.43%), Space: 18.5 MB (85.36%) - LeetHub

---
 .../0025-reverse-nodes-in-k-group.py          | 68 +++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 0025-reverse-nodes-in-k-group/0025-reverse-nodes-in-k-group.py

diff --git a/0025-reverse-nodes-in-k-group/0025-reverse-nodes-in-k-group.py b/0025-reverse-nodes-in-k-group/0025-reverse-nodes-in-k-group.py
new file mode 100644
index 0000000..4ae53aa
--- /dev/null
+++ b/0025-reverse-nodes-in-k-group/0025-reverse-nodes-in-k-group.py
@@ -0,0 +1,68 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
+        if k == 1:
+            return head
+
+        dummyHead = ListNode(-1, head)
+
+        beforeSeg = dummyHead
+        firstInSeg = head
+        lastInSeg = None
+        afterSeg = None
+
+        # Get initial values for lastInSeg and afterSeg
+        curr = head
+        for i in range(k):
+            if i == k - 1:
+                lastInSeg = curr
+                afterSeg = curr.next
+            elif curr is None:
+                return head
+
+            curr = curr.next
+        
+
+        # hold one before segment
+        # hold last in segment
+        # hold one after segment
+
+        while lastInSeg is not None:
+            # in segment, flip all links
+            prev = None
+            curr = beforeSeg.next
+            next = beforeSeg.next.next
+
+            for i in range(k):
+                newPrev = curr
+                newCurr = next
+                newNext = next.next if next is not None else None
+
+                curr.next = prev
+
+                prev, curr, next = newPrev, newCurr, newNext
+
+            
+            beforeSeg.next = lastInSeg
+            firstInSeg.next = afterSeg
+
+            beforeSeg = firstInSeg
+            firstInSeg = afterSeg
+
+            curr = firstInSeg
+            lastInSeg = None
+            afterSeg = None
+            for i in range(k):
+                if curr is None:
+                    break
+                elif i == k - 1:
+                    lastInSeg = curr
+                    afterSeg = curr.next
+
+                curr = curr.next
+
+        return dummyHead.next
\ No newline at end of file