合併兩個有序鏈表(Leetcode)

problem address

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

我們可以讓兩個指針i,j分別指向了兩個鏈表的頭結點然後比較值，然後++ 操作，
最後還可能有剩餘的鏈表節點沒有合併，合併返回頭結點即可。

# 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:
        root = ListNode(None)
        cur = root 
        while l1 and l2:
            if l1.val < l2.val:
                node = ListNode(l1.val)
                l1 = l1.next
            else:
                node = ListNode(l2.val)
                l2 = l2.next 
            cur.next = node 
            cur = node 
        cur.next = l1 or l2 
        return root.next