LeetCode-21 - Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

Solution

• 同时遍历两个列表用while l1 or l2
• 两个列表判空，分3中case, l1 and l2; l1; l2

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

class Solution(object):
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        result = ListNode(0)
        node = result
        while l1 or l2:
            if l1 and l2:
                if l1.val < l2.val:
                    node.next = ListNode(l1.val)
                    l1 = l1.next
                else:
                    node.next = ListNode(l2.val)
                    l2 = l2.next
            elif l1:
                node.next = ListNode(l1.val)
                l1 = l1.next
            elif l2:
                node.next = ListNode(l2.val)
                l2 = l2.next
            node = node.next
        return result.next