❤ Leetcode,python2❤ Merge two ordered lists into a new ordered list and return. A new list is formed by concatenating all the nodes of a given two lists.

class Solution(object):
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if l1==None and l2==None:
            return None
        if l1==None:
            return l2
        if l2==None:
            return l1
        if l1.val<l2.val:
            l1.next = self.mergeTwoLists(l1.next,l2)
            return l1
        if l2.val<l1.val:
            l2.next = self.mergeTwoLists(l1,l2.next)
            return l2
        elif l1.val==l2.val:
            l1.next = self.mergeTwoLists(l1.next,l2)
            return l1
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