1->2->3->4
转换成2->1->4->3
.
class ListNode: def __init__( self , x): self .val = x self . next = None class Solution: # @param a ListNode # @return a ListNode def swapPairs( self , head): if head ! = None and head. next ! = None : next = head. next head. next = self .swapPairs( next . next ) next . next = head return next return head |