【leetcode】剑指 Offer 25. 合并两个排序的链表（python）

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

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:    # 已AC        
        if not l1: return l2
        if not l2: return l1
        if l1.val <= l2.val:  # 用l1或者l2中头结点较小的那个作为返回链表的头结点
            res = l1
            l1 = l1.next
        else:
            res = l2
            l2 = l2.next
        p = res
        while l1 and l2:
            if l1.val <= l2.val:
                p.next = l1
                l1 = l1.next
            else:
                p.next = l2
                l2 = l2.next
            p = p.next
        if not l1:
            p.next = l2
        if not l2:
            p.next = l1
        return res

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        if not l1: return l2
        if not l2: return l1
        dummy = ListNode(0)
        cur = dummy
        while l1 and l2:
            if l1.val <= l2.val:
                cur.next = l1
                l1 = l1.next
            else:
                cur.next = l2
                l2 = l2.next
            cur = cur.next
        cur.next = l1 if l1 else l2
        return dummy.next