题目
Merge 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.
题解
这道题是经典的考察链表的题目。
解法一：递归
- 终止条件：两条链表分别名为
l1和l2，当l1为空或l2为空时结束 - 返回值：每一层调用都返回排序好的链表头
- 本级递归内容：如果
l1的val值更小，则将l1.next与排序好的链表头相接，l2同理 -
O(m+n)O(m+n)，mm为l1的长度，nn为l2的长度
//Go
/**
* Definition for singly-linked list.
* type ListNode struct {
* Val int
* Next *ListNode
* }
*/
func mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {
if l1 == nil {
return l2;
}else if l2 == nil {
return l1;
}else if (l1.Val < l2.Val) {
l1.Next = mergeTwoLists(l1.Next, l2);
return l1;
}else {
l2.Next = mergeTwoLists(l1, l2.Next);
return l2;
}
}
执行结果：
leetcode-cn：
执行用时：0 ms, 在所有 Go 提交中击败了100.00%的用户
内存消耗：2.6 MB, 在所有 Go 提交中击败了26.43%的用户
leetcode：
Runtime: 0 ms, faster than 100.00% of Go online submissions for Merge Two Sorted Lists.
Memory Usage: 2.6 MB, less than 51.09% of Go online submissions for Merge Two Sorted Lists.
可以看到，该解法执行用时为0ms，非常高效。