Update solution 024 [Python3]

Author: chakyam

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

@@ -0,0 +1,28 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution:
+    def swapPairs(self, head):
+        """
+        :type head: ListNode
+        :rtype: ListNode
+        """
+        if (not head) or (not head.next):
+            return head
+        pre=head.next
+        p=head
+        q=head.next
+        
+        while q:
+            t=q.next
+            q.next=p
+            if (not t) or (not t.next):
+                p.next=t
+                break
+            p.next=t.next
+            p=t
+            q=p.next
+        return pre