[数据结构与算法]剑指 Offer 25. 合并两个排序的链表（双指针）

题目描述

双指针

# 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:
        if not l1:
            return l2
        if not l2:
            return l1
        node1, node2 = l1, l2
        if l1.val <= l2.val:
            head = l1
            node1 = node1.next
        else:
            head = l2
            node2 = node2.next
        node = head
        while node1 and node2:
            if node1.val <= node2.val:
                node.next = node1
                node = node.next
                node1 = node1.next
            else:
                node.next = node2
                node = node.next
                node2 = node2.next
        # 若node1遍历完
        if not node1:
            node.next = node2
        if not node2:
            node.next = node1
        return head

更简洁的写法，参考

# 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:
        cur = dum = ListNode(0) # 伪头节点
        while l1 and l2:
            if l1.val < l2.val:
                cur.next = l1
                l1 = l1.next
            else:
                cur.next = l2
                l2 = l2.next
            cur = cur.next
        cur.next = l1 if l1 else l2
        return dum.next