Merge k Sorted Lists

最新推荐文章于 2021-12-08 15:59:42 发布

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本文介绍了一种使用堆来解决K路归并链表问题的方法。通过将多个已排序的链表合并成一个单一的排序链表，该算法有效地处理了复杂度，并提供了清晰的实现步骤。

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.

K路归并算法，使用heap的方式处理

/**
 * 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;
        }
        ListNode dummy = new ListNode(0);
        ListNode head = dummy;
        Comparator<ListNode> cmp = new Comparator<ListNode>() {
            public int compare(ListNode a, ListNode b) {
                return a.val - b.val;
            }  
        };
        PriorityQueue<ListNode> heap = new PriorityQueue<>(10, cmp);
        for (int i = 0; i < lists.size(); i++) {
            ListNode node =  lists.get(i);
            while (node != null) {
                heap.offer(node);
                node = node.next;
            }
        }
        while (!heap.isEmpty()) {
            head.next = heap.poll();
            head = head.next;
        }
        return dummy.next;
    }
}