0021: Merge Two Sorted Lists

Problem Statement

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

Merge the two lists into 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.

Code Solution

class Solution:
    def mergeTwoLists(self, list1, list2):
        dummy = ListNode(0)
        
        temp = dummy
        while list1 or list2:
            v1 = float('inf') if not list1 else list1.val
            v2 = float('inf') if not list2 else list2.val
            if v1 > v2:
                temp.next = ListNode(v2)
                list2 = None if not list2 else list2.next
            else:
                temp.next = ListNode(v1)
                list1 = None if not list1 else list1.next
            temp = temp.next
        
        return dummy.next