Leetcode题库——21.合并两个有序链表

---

@author: ZZQ
@software: PyCharm
@file: mergeTwoLists.py
@time: 2018/9/16 20:49
要求：将两个有序链表合并为一个新的有序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。
e.g.:
输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4

# Definition for singly-linked list.
class ListNode(object):
    def __init__(self, x):
        self.val = x
        self.next = None


class Solution():
    def __init__(self):
        pass

    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if l1 is None and l2 is None:
            return None

        if l1 is None:
            return l2

        if l2 is None:
            return l1

        l3 = ListNode(0)
        head = l3
        while l1 is not None and l2 is not None:
            if l1.val > l2.val:
                head.next = l2
                l2 = l2.next
            else:
                head.next = l1
                l1 = l1.next
            head = head.next
        if l1 is not None and l2 is None:
            head.next = l1

        if l1 is None and l2 is not None:
            head.next = l2
        return head.next