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Author: assassint2017

Reverse Nodes in k-Group/Reverse_Nodes_in_k_Group.py

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+# 56ms 96.14%
+class Solution:
+    def reverseKGroup(self, head, k):
+        """
+        :type head: ListNode
+        :type k: int
+        :rtype: ListNode
+        """
+        if not head:
+            return None
+        
+        mid = head
+        stack, flag, last_node = [], True, ListNode(0)
+        
+        while True:
+            for i in range(k):
+                stack.append(mid)
+                mid = mid.next
+                if mid is None and i < k - 1:
+                    return head
+            
+            reverse_head = reverse_mid = stack.pop()
+            
+            if flag:
+                head = reverse_mid
+                flag = False
+            
+            while stack:    
+                reverse_mid.next = stack.pop()
+                reverse_mid = reverse_mid.next
+            
+            reverse_mid.next = mid
+            last_node.next = reverse_head
+            last_node = reverse_mid
+
+            if mid is None:
+                return head