• 用递归的方法，注意这里的pMeargedHead进入每一次迭代后都设置为None 
class Solution:
    # 返回合并后列表
    def Merge(self, pHead1, pHead2):
        # write code here
        pMergedHead = None
        if pHead1 == None:return pHead2
        elif pHead2 == None:return pHead1
        if pHead1.val < pHead2.val:
            pMergedHead = pHead1
            pMergedHead.next = self.Merge(pHead1.next, pHead2)
        else:
            pMergedHead = pHead2
            pMergedHead.next = self.Merge(pHead1, pHead2.next)
        return pMergedHead