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23.merge-k-sorted-lists.cpp
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23.merge-k-sorted-lists.cpp
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/*
* @lc app=leetcode id=23 lang=cpp
*
* [23] Merge k Sorted Lists
*
* https://leetcode.com/problems/merge-k-sorted-lists/description/
*
* algorithms
* Hard (35.36%)
* Likes: 2732
* Dislikes: 175
* Total Accepted: 425.1K
* Total Submissions: 1.2M
* Testcase Example: '[[1,4,5],[1,3,4],[2,6]]'
*
* Merge k sorted linked lists and return it as one sorted list. Analyze and
* describe its complexity.
*
* Example:
*
*
* Input:
* [
* 1->4->5,
* 1->3->4,
* 2->6
* ]
* Output: 1->1->2->3->4->4->5->6
*
*
*/
/**
* 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()(const ListNode* p1, const ListNode* p2) {
return p1 -> val > p2 -> val;
}
};
ListNode* mergeKLists(vector<ListNode*>& lists) {
ListNode *root = nullptr;
priority_queue<ListNode*, vector<ListNode*>, cmp> nodes;
for (auto item : lists) {
if (item) {
nodes.push(item);
}
}
if (!nodes.empty()) {
root = nodes.top();
nodes.pop();
if (root -> next) {
nodes.push(root -> next);
}
}
ListNode *p = root;
while (!nodes.empty()) {
p -> next = nodes.top();
nodes.pop();
p = p -> next;
if (p -> next) {
nodes.push(p -> next);
}
}
return root;
}
};