23. 合并K个排序链表

题目描述

合并 k 个排序链表，返回合并后的排序链表。请分析和描述算法的复杂度。

示例:

输入:
[
  1->4->5,
  1->3->4,
  2->6
]

输出: 1->1->2->3->4->4->5->6

分析

通过优先级队列查找K个有序链表中的最小元素表头，链接到有序链表中去，表头把下一个元素插入到优先级队列

代码

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
struct cmp {
    bool operator () (ListNode * a, ListNode * b) {
        return a->val > b->val;
    }
};
 
class Solution {  
public:  
    ListNode *mergeKLists(vector &lists) {  
        priority_queue, cmp> q;
        for (int i = 0; i < lists.size(); ++i) {
            if (lists[i] != NULL) {
                q.push(lists[i]);
            }
        }
        ListNode dumy(0);
        auto* head = &dumy;
        while (!q.empty()) {
            auto& tmp = q.top();
            head->next = tmp;
            head = head->next;
            if(tmp->next != NULL) {
                q.push(tmp->next);
            }
            q.pop();
        }
        return dumy.next;
    }  
};

题目链接

https://leetcode-cn.com/problems/merge-k-sorted-lists/description/