旭的小窝

21. Merge Two Sorted Lists

 
  • 2023年 06月24日

Promble

link: https://leetcode.com/problems/merge-two-sorted-lists

You are given the heads of two sorted linked lists list1 and list2.

Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two lists.

Return the head of the merged linked list.

Input: list1 = [1,2,4], list2 = [1,3,4]
Output: [1,1,2,3,4,4]

Input: list1 = [], list2 = []
Output: []

Input: list1 = [], list2 = [0]
Output: [0]

Approach

Thought

  1. def cur and dummy, is the ListNode()
  2. while list1 and list2 is not None
    1. if list1.val < list2.val
      1. cur.next = list1
      2. list1, cur = list1.next, list1
    2. else:
      1. cur.next = list2
      2. list2, cur = list2.next, list2
    3. final check: if list1 or list2: cur.next = list1 if list1 else list2
  3. return dummy.next # dummy start with 0.

Code


# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
        cur = dummy = ListNode()
        print(cur)
        while list1 and list2:
            if list1.val < list2.val:
                cur.next = list1
                list1, cur = list1.next, list1

            else:
                cur.next = list2
                list2, cur = list2.next, list2

        if list1 or list2:
            cur.next = list1 if list1 else list2

        print(dummy)
        return dummy.next
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