Method swapPairs2

leetcode/24. Swap Nodes in Pairs.py:34–43

(self, head)

        return head
    # recursion
    def swapPairs2(self, head):
        if not head or not head.next:
            return head

        first, second = head, head.next
        third = second.next
        head = second
        second.next = first
        first.next = self.swapPairs(third)
        return head