[LeetCode&Python] Problem 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

# 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
        """
        if not l1 and l2:
            return l2
        if not l2 and l1:
            return l1
        if not l1 and not l2:
            return []

        it1=l1
        it2=l2
        if it1.val<=it2.val:
            node=ListNode(it1.val)
            it1=it1.next
        else:
            node=ListNode(it2.val)
            it2=it2.next
        ll=node
        while it1 and it2:
            if it1.val<=it2.val:
                node1=ListNode(it1.val)
                it1=it1.next
                node.next=node1
                node=node1
            else:
                node1=ListNode(it2.val)
                node.next=node1
                node=node1
                it2=it2.next

        if it1:
            node.next=it1
        elif it2:
            node.next=it2
        return ll