Ruby solution for 024

Author: MarkKuang1991

solution/024.Swap Nodes in Pairs/Solution.rb

@@ -0,0 +1,23 @@
+# Definition for singly-linked list.
+# class ListNode
+#     attr_accessor :val, :next
+#     def initialize(val)
+#         @val = val
+#         @next = nil
+#     end
+# end
+
+# @param {ListNode} head
+# @return {ListNode}
+def swap_pairs(head)
+  if head.nil? || head.next.nil?
+    return head
+  end
+
+  res = head.next
+  tmp = head.next.next
+  head.next.next = head
+  head.next = swap_pairs(tmp)
+
+  res
+end