148

/**
 * 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:
    struct compare{
        bool operator()(const ListNode* a, const ListNode* b){
            return a->val > b->val;
        }
    };

    ListNode* sortList(ListNode* head) {
        priority_queue<ListNode*, vector<ListNode*>, compare> pq;
        ListNode *dummy = new ListNode(0);
        while(head){
            pq.push(head);
            head = head->next;
        }
        ListNode *curr = dummy;
        while(!pq.empty()){
            curr->next = pq.top();
            pq.pop();
            curr = curr->next;
        }
        curr->next = NULL;
        return dummy->next;
    }
};