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_0023_MergeKSortedLists.java
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_0023_MergeKSortedLists.java
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package com.diguage.algorithm.leetcode;
import java.util.*;
import com.diguage.algorithm.util.ListNode;
import static com.diguage.algorithm.util.ListNodeUtils.*;
/**
* = 23. Merge k Sorted Lists
*
* https://leetcode.com/problems/merge-k-sorted-lists/[(8) Merge k Sorted Lists - LeetCode]
*
* Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
*
* .Example:
* [source]
* ----
* Input:
* [
* 1->4->5,
* 1->3->4,
* 2->6
* ]
* Output: 1->1->2->3->4->4->5->6
* ----
*
* @author D瓜哥, https://www.diguage.com/
* @since 2019-10-22 12:40:12
*/
public class _0023_MergeKSortedLists {
public ListNode mergeKLists(ListNode[] lists) {
PriorityQueue<ListNode> heap = new PriorityQueue<>((l1, l2) -> l1.val - l2.val);
for (ListNode l : lists) {
if (Objects.nonNull(l)) {
heap.add(l);
}
}
ListNode dummy = new ListNode();
ListNode curr = dummy;
while (!heap.isEmpty()) {
ListNode node = heap.poll();
curr.next = node;
curr = curr.next;
if (Objects.nonNull(node.next)) {
heap.add(node.next);
}
}
return dummy.next;
}
/**
* Runtime: 40 ms, faster than 20.21% of Java online submissions for Merge k Sorted Lists.
*
* Memory Usage: 39.6 MB, less than 74.87% of Java online submissions for Merge k Sorted Lists.
*/
public ListNode mergeKLists1(ListNode[] lists) {
PriorityQueue<ListNode> queue = new PriorityQueue<>(Comparator.comparingInt(o -> o.val));
for (ListNode list : lists) {
if (Objects.nonNull(list)) {
queue.add(list);
}
}
ListNode result = null;
ListNode tail = null;
for (ListNode node = queue.poll(); Objects.nonNull(node); ) {
if (Objects.isNull(result)) {
result = node;
}
ListNode next = node.next;
if (Objects.nonNull(next)) {
queue.add(next);
}
if (Objects.nonNull(tail)) {
tail.next = node;
}
tail = node;
node = queue.poll();
}
return result;
}
public static void main(String[] args) {
ListNode node1 = build(Arrays.asList(1, 4, 5));
ListNode node2 = build(Arrays.asList(1, 3, 4));
ListNode node3 = build(Arrays.asList(2, 6));
ListNode[] lists = new ListNode[]{node1, node2, node3};
_0023_MergeKSortedLists solution = new _0023_MergeKSortedLists();
ListNode r1 = solution.mergeKLists(lists);
System.out.println(isOrder(r1));
}
}