23. Merge k Sorted Lists***
https://leetcode.com/problems/merge-k-sorted-lists/
题目描述
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
C++ 实现 1
使用最小堆处理. 注意输入可能是 [nullptr]
的情况, 因此在下面代码中, 加入了 if (l)
的判断.
class Solution {
private:
struct Comp {
bool operator()(ListNode *p1, ListNode *p2) {
return p1->val > p2->val;
}
};
public:
ListNode* mergeKLists(vector<ListNode*>& lists) {
priority_queue<ListNode*, vector<ListNode*>, Comp> q;
ListNode *dummy = new ListNode(0);
auto ptr = dummy;
for (auto &l : lists)
if (l)
q.push(l);
while (!q.empty()) {
auto l = q.top();
q.pop();
ptr->next = l;
ptr = ptr->next;
if (l->next) q.push(l->next);
}
return dummy->next;
}
};