21. Merge Two Sorted Lists

📋 Đề Bài

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.

Example 1:

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

Example 2:

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

Example 3:

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

Constraints:

The number of nodes in both lists is in the range [0, 50].
-100 <= Node.val <= 100
Both list1 and list2 are sorted in non-decreasing order.

🧠 Thuật Toán & Kỹ Thuật

Linked List (Danh sách liên kết)

⏱️ Thời gian O(n)

💾 Không gian O(n)

💻 Lời Giải

Python 0021-merge-two-sorted-lists.py

# 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]:
        list3 = ListNode(0)
        i, j, k = list1, list2, list3
        
        while i and j:
            if i.val < j.val:
                k.next = ListNode(i.val)
                i = i.next
            else:
                k.next = ListNode(j.val)
                j = j.next
            k = k.next
            
        k.next = i if i else j
        
        return list3.next