LeetCode 23. Merge k Sorted Lists
Priority Queue | Linked List
You are given an array of k
linked-lists lists
, each linked-list is sorted in ascending order.
Merge all the linked-lists into one sorted linked-list and return it.
Example 1:
Input: lists = [[1,4,5],[1,3,4],[2,6]]
Output: [1,1,2,3,4,4,5,6]
Explanation: The linked-lists are:
[
1->4->5,
1->3->4,
2->6
]
merging them into one sorted list:
1->1->2->3->4->4->5->6
Example 2:
Input: lists = []
Output: []
Example 3:
Input: lists = [[]]
Output: []
Constraints:
k == lists.length
0 <= k <= 10^4
0 <= lists[i].length <= 500
-10^4 <= lists[i][j] <= 10^4
lists[i]
is sorted in ascending order.The sum of
lists[i].length
won't exceed10^4
.
Solution:
class Solution {
public:
ListNode *mergeKLists(vector<ListNode *> &lists) {
auto cmp = [] (ListNode *n1, ListNode *n2) {
return n1->val > n2->val;
};
priority_queue<ListNode*, vector<ListNode*>, decltype(cmp)> nodes(cmp);
for (ListNode *list : lists) {
if (list != nullptr) {
nodes.push(list);
}
}
if (nodes.empty()) {
return nullptr;
}
ListNode fake_head(0);
ListNode* current = &fake_head;
while (!nodes.empty()) {
current->next = nodes.top();
current = current->next;
nodes.pop();
if (current->next != nullptr) {
nodes.push(current->next);
}
}
return fake_head.next;
}
};
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