力扣23. 合并K个升序链表

Posted 2021-06-27 幽殇默

题目地址

/**
 * 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:
    priority_queue<int, vector<int>, greater<int> > heap;
    ListNode* mergeKLists(vector<ListNode*>& lists) 
    {
        ListNode* head=new ListNode(-1);
        ListNode* temp=head;
        for(int i=0;i<lists.size();i++)
        {
            while(lists[i])
            {
                heap.push(lists[i]->val);
                lists[i]=lists[i]->next;
            }
        }
        while(heap.size())
        {
            temp=temp->next=new ListNode(heap.top());
            heap.pop();
        }
        return head->next;
    }
};

y总方法：

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
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;
    }
};