LeetCode Merge k Sorted Lists

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

题意：将k个已经排好序的链表合并成一个

思路：用到优先队列比较简单。

/** * 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<ListNode *> &lists) {        priority_queue<ListNode *, vector<ListNode *>, cmp> queue;        for (int i = 0; i < lists.size(); i++) {            if (lists[i] != NULL)                queue.push(lists[i]);        }         ListNode *head = NULL, *pre = NULL, *tmp;        while (!queue.empty()) {            tmp = queue.top();            queue.pop();            if (pre == NULL) head = tmp;            else pre->next = tmp;            pre = tmp;            if (tmp->next != NULL)                queue.push(tmp->next);        }        return head;    }};