merge-two-sorted-lists.py

# Definition for singly-linked list.
class ListNode(object):
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next


class Solution(object):
    def mergeTwoLists(self, list1: ListNode, list2: ListNode):
        """
        :type list1: Optional[ListNode]
        :type list2: Optional[ListNode]
        :rtype: Optional[ListNode]
        """
        prehead = ListNode(-1)
        prev = prehead
        while list1 and list2:
            if list1.val <= list2.val:
                prev.next = list1
                list1 = list1.next
            else:
                prev.next = list2
                list2 = list2.next
            prev = prev.next
        prev.next = list1 if list1 is not None else list2
        return prehead.next

# 第二次做 这道题
# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next


class Solution:
    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
        dummy = ListNode(-1)
        p = dummy
        p1 = list1
        p2 = list2
        while p1 is not None and p2 is not None:
            if p1.val > p2.val:
                p.next = p2
                p2 = p2.next
            else:
                p.next = p1
                p1 = p1.next
            p = p.next
        if p1 is not None:
            p.next = p1
        if p2 is not None:
            p.next = p2
        return dummy.next


if __name__ == '__main__':
    # l1 = [1,2,4]
    l1 = ListNode(1)
    l1.next = ListNode(2)
    l1.next.next = ListNode(4)
    # l2 = [1,3,4]
    l2 = ListNode(1)
    l2.next = ListNode(3)
    l2.next.next = ListNode(4)
    a = Solution()
    a.mergeTwoLists(l1, l2)