23 合并 K 个升序链表

https://leetcode.cn/leetbook/read/top-interview-questions-hard/xwcdnh/

cost: 12m37s

/**
 * 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) {}
 * };
 */

struct CustomComparator {
    bool operator()(ListNode* a, ListNode* b) { return a->val > b->val; }
};

class Solution {
public:
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        priority_queue<ListNode*, std::vector<ListNode*>, CustomComparator> q;
        for (const auto head : lists) {
            if (head != nullptr) {
                q.push(head);
            }
        }
        ListNode head = ListNode{};
        head.next = nullptr;
        ListNode* p = &head;
        while (!q.empty()) {
            p->next = q.top();
            p = p->next;
            q.pop();
            if (p != nullptr && p->next != nullptr) {
                q.push(p->next);
            }
        }
        return head.next;
    }
};