21. Merge Two Sorted Lists

2019-03-31

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:

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

Code1:

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

class Solution:
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if not l1:return l2
        if not l2:return l1

        start = None    
        if l1.val < l2.val:
            start = l1;
            start.next = self.mergeTwoLists(l1.next, l2)
        else:
            start = l2;
            start.next = self.mergeTwoLists(l1, l2.next)

        return start

Code2:

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class Solution:
    def mergeTwoLists(self, a, b):
        if a and b:
            if a.val > b.val:
                a, b = b, a
            a.next = self.mergeTwoLists(a.next, b)
        return a or b
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