LeetCode | 21.合并两个有序链表

这道题也是很经典的一道题了，408的算法题中也考过这个思想，因为两个链表已是升序，合并只需要两个指针，分别指向两个表的表头，分别比较两个指针所指向的结点的val，小的就插入到目标链表里面，再后移相应指针，直到有一个链表为空，再把剩下的非空链表全部查到目标链表后面即可

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):def mergeTwoLists(self, list1, list2):""":type list1: Optional[ListNode]:type list2: Optional[ListNode]:rtype: Optional[ListNode]"""ans = ListNode()current = ansi = list1j = list2while i is not None and j is not None:if i.val <= j.val:current.next = ListNode(i.val)i = i.nextelse:current.next = ListNode(j.val)j = j.nextcurrent = current.nextcurrent.next = i if i is not None else jreturn ans.next