Merge k Sorted Lists

最新推荐文章于 2021-12-08 15:59:42 发布

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本文介绍了一种使用最小堆实现的高效算法来合并多个已排序的链表，并详细展示了如何利用C++标准模板库中的优先队列实现该算法。

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Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
bool operator <(const pair<ListNode*,int> &p1, const pair<ListNode*,int> &p2){
    return p1.first->val < p2.first->val;
}

/*假设投针数组为副本，且由其它地方销毁*/
#include<queue>
class Solution {
public:
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        ListNode* helpNode = new ListNode(0);
        ListNode* cur = helpNode;

        typedef pair<ListNode*,int> heaptype;
        priority_queue<heaptype,vector<heaptype>,greater<heaptype>> q;//最小队列
        for(int i = 0; i< lists.size(); ++i){
            if(lists[i]){
                q.push(make_pair(lists[i],i));
                lists[i] = lists[i]->next;
            }
        }

        while(!q.empty()){
            ListNode* node = q.top().first;
            int index = q.top().second;
            q.pop();

            if(lists[index]){
                q.push(make_pair(lists[index],index));
                lists[index] = lists[index]->next;
            }

            cur->next = new ListNode(node->val);
            cur= cur->next;
        }
        
        auto ret = helpNode->next;
        delete helpNode;
        return ret;


    }
};