21. Merge Two Sorted Lists
Category: /leetcodeMerge two sorted linked lists and return it as a sorted list. The list should be made by splicing together the nodes of the first two lists.
Example 1:
Input: l1 = [1,2,4], l2 = [1,3,4]
Output: [1,1,2,3,4,4]
Example 2:
Input: l1 = [], l2 = []
Output: []
Example 3:
Input: l1 = [], l2 = [0]
Output: [0]
Constraints:
The number of nodes in both lists is in the range [0, 50].
-100 <= Node.val <= 100
Both l1 and l2 are sorted in non-decreasing order.
Solution
Iteration
T: O(m + n), S:O(1)
def mergeTwoLists(self, l1, l2):
prehead = ListNode(-1)
curr = prehead
while l1 and l2:
if l1.val < l2.val:
curr.next = l1
l1 = l1.next
else:
curr.next = l2
l2 = l2.next
curr = curr.next
curr.next = l1 or l2
return prehead.next
Recursion
T: O(m + n), S:O(m + n)
def mergeTwoList(self, l1, l2):
if not l1: return l2
if not l2: return l1
if l1.val < l2.val:
l1.next = self.mergeTwoList(l1.next, l2)
return l1
else:
l2.next = self.mergeTwoList(l1, l2.next)
return l2
