reverse_k_group

Author: Bhuvana-ai-ml

reverse_k_group.rb

@@ -0,0 +1,38 @@
+# Definition for singly-linked list.
+# class ListNode
+#     attr_accessor :val, :next
+#     def initialize(val = 0, _next = nil)
+#         @val = val
+#         @next = _next
+#     end
+# end
+
+def reverse_k_group(head, k)
+  return head if head.nil? || k == 1
+
+  dummy = ListNode.new(0)
+  dummy.next = head
+  prev_group = dummy
+
+  while true
+    kth = prev_group
+    k.times do
+      kth = kth.next
+      return dummy.next if kth.nil?
+    end
+
+    group_next = kth.next
+    prev, curr = group_next, prev_group.next
+
+    while curr != group_next
+      temp = curr.next
+      curr.next = prev
+      prev = curr
+      curr = temp
+    end
+
+    temp = prev_group.next
+    prev_group.next = kth
+    prev_group = temp
+  end
+end