LeetCode_Everyday：021 Merge Two Sorted Lists

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题目:

将两个升序链表合并为一个新的升序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。

示例：

• 示例 1:

  输入：1->2->4, 1->3->4
  输出：1->1->2->3->4->4
  

代码

方法一： 递归 题解

执行用时：56 ms, 在所有 Python3 提交中击败了18.41%的用户
内存消耗：13.7 MB, 在所有 Python3 提交中击败了7.14%的用户

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

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        if l1 and l2:
            if l1.val > l2.val: l1, l2 = l2, l1
            l1.next = self.mergeTwoLists(l1.next, l2)
        return l1 or l2

"""
For Example:    input:    l1:1->2->4  l2:1->3->4
               output:    1->1->2->3->4->4
"""
l1 = ListNode(1)
l1.next = ListNode(2)
l1.next.next = ListNode(4)
l2 = ListNode(1)
l2.next = ListNode(3)
l2.next.next = ListNode(4)
                
solution = Solution()
result = solution.mergeTwoLists(l1, l2)
print('输出为：%d->%d->%d->%d->%d->%d' % \
      (result.val, result.next.val, result.next.next.val, result.next.next.next.val,\
      result.next.next.next.next.val, result.next.next.next.next.next.val))

方法二： 递循环遍历 题解

执行用时：44 ms, 在所有 Python3 提交中击败了79.61%的用户
内存消耗：13.8 MB, 在所有 Python3 提交中击败了7.14%的用户

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

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        dummy = ListNode(0)
        move = dummy
        while l1 and l2:
            if l1.val <= l2.val:
                move.next = l1
                l1 = l1.next
            else:
                move.next = l2
                l2 = l2.next
            move = move.next
        move.next = l1 if l1 else l2
        return dummy.next

"""
For Example:    input:    l1:1->2->4  l2:1->3->4
               output:    1->1->2->3->4->4
"""
l1 = ListNode(1)
l1.next = ListNode(2)
l1.next.next = ListNode(4)
l2 = ListNode(1)
l2.next = ListNode(3)
l2.next.next = ListNode(4)
                
solution = Solution()
result = solution.mergeTwoLists(l1, l2)
print('输出为：%d->%d->%d->%d->%d->%d' % \
      (result.val, result.next.val, result.next.next.val, result.next.next.next.val,\
      result.next.next.next.next.val, result.next.next.next.next.next.val))
      

参考

1. https://leetcode-cn.com/problems/merge-two-sorted-lists/solution/yi-kan-jiu-hui-yi-xie-jiu-fei-xiang-jie-di-gui-by-/
2. https://leetcode-cn.com/problems/merge-two-sorted-lists/solution/xin-shou-you-hao-xue-hui-tao-lu-bu-fan-cuo-4nian-l/

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