放到數組裡排序就行了

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public
 
:
    int a[50010];
    ListNode* sortList(ListNode* head) {
        if (head == nullptr) return head;
        ListNode* p = head;
        int cnt = 0;
        while(p != nullptr)
        {
            a[cnt++] = p->val;
            p = p->next;
        }
        sort(a, a + cnt);
        p = head;
        cnt 
 
= 0;
        while(p != nullptr)
        {
            p->val = a[cnt++];
            p = p->next;
        }
        
        return head;

    }
};