Mind palace

some thoughts

0%

148. Sort List

Posted on Edited on In Disqus:
Symbols count in article: 827 Reading time ≈ 1 mins.

merge sort O(nlogn) time

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* sortList(ListNode* head) {
        if (!head || !head->next) return head;
        ListNode dummy_head(0), *slow = &dummy_head, *fast = slow;
        dummy_head.next = head;
        while (fast && fast->next) {
            slow = slow->next;
            fast = fast->next->next;
        }
        auto l1 = head, l2 = slow->next;
        slow->next = nullptr;
        l1 = sortList(l1);
        l2 = sortList(l2);
        auto tail = &dummy_head;
        while (l1 && l2) {
            if (l1->val < l2->val) {
                tail->next = l1;
                l1 = l1->next;
            } else {
                tail->next = l2;
                l2 = l2->next;
            }
            tail = tail->next;
        }
        tail->next = l1 ? l1 : l2;
        return dummy_head.next;
    }
};