day84（2.12）——leetcode面试经典150

23. 合并 K 个升序链表

23. 合并K个升序链表

题目：

题解：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
        ListNode root = new ListNode();
        List<Integer> list = new ArrayList<>();
        for(int i=0;i<lists.length;i++) {
            ListNode node = lists[i];
            ListNode cur = node;
            while(cur != null) {
                list.add(cur.val);
                cur = cur.next;
            }
        }
        if (list.isEmpty()) {
            return null;
        }
        list.sort(null);
        ListNode t = new ListNode();
        ListNode c = t;
        for(int i=0;i<list.size();i++) {
            t.val = list.get(i);
            if(i!=list.size()-1) {
                t.next = new ListNode();
            }
            else {
                t.next = null;
            }
            t = t.next;
        }
        return c;
    }
}