Merge k Sorted Lists

最新推荐文章于 2019-10-31 10:48:55 发布

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最新推荐文章于 2019-10-31 10:48:55 发布

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分类专栏： leetcode 文章标签：标签 path class

本文链接：https://blog.youkuaiyun.com/sinat_32547403/article/details/78639613

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本文介绍了一种使用堆（Heap）来合并K个已排序链表的有效算法，并提供了详细的实现步骤与代码示例。

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Merge k sorted linked lists and return it as one sorted list.

Analyze and describe its complexity.

Have you met this question in a real interview?

Yes

Example

Given lists:

[
  2->4->null,
  null,
  -1->null
],

return -1->2->4->null.

该题目使用heap的方法去做，首先将lists中的所用节点放到heap中，然后分别将listnode中的节点向后移动，直到null

/**
 * Definition for ListNode.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int val) {
 *         this.val = val;
 *         this.next = null;
 *     }
 * }
 */ 
public class Solution {
    /**
     * @param lists: a list of ListNode
     * @return: The head of one sorted list.
     */
    public ListNode mergeKLists(List<ListNode> lists) {  
        // write your code here
        if (lists == null || lists.size() == 0) {
            return null;
        }
        Comparator<ListNode> cmp = new Comparator<ListNode>() {
            public int compare(ListNode a, ListNode b) {
                return a.val - b.val;
            }
        };
        Queue<ListNode> pq = new PriorityQueue<>(lists.size(), cmp);
        for (int i = 0; i < lists.size(); i++) {
            if (lists.get(i) != null) {
                pq.offer(lists.get(i));
            }
        }
        ListNode dummy = new ListNode(-1);
        ListNode head = dummy;
        ListNode node = null;
        while (!pq.isEmpty()) {
            node = pq.poll();
            head.next = node;
            head = head.next;
            if (node.next != null) {
                pq.offer(node.next);
            }
        }
        return dummy.next;
    }
}