23. 合并 K 个升序链表(LeetCode困难)(链表\数据结构)

23. 合并 K 个升序链表
使用堆

/**
 * 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 Cmp{
        bool operator() (ListNode *a, ListNode *b){
            return a->val > b->val;
        }
    };
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        priority_queue<ListNode*, vector<ListNode*>, Cmp> heap;
        auto dummy = new ListNode(-1), tail = dummy;
        for(auto l : lists) if(l) heap.push(l);
        
        while(heap.size()){
            auto t = heap.top(); heap.pop();
            tail = tail->next = t;
            if(t->next) heap.push(t->next);
        }  

        return dummy->next;
    }
};