23.合并K个升序链表 0

题目：
给你一个链表数组，每个链表都已经按升序排列。请你将所有链表合并到一个升序链表中，返回合并后的链表。

代码1：
/**

• Definition for singly-linked list.
• public class ListNode {

• int val;
  

• ListNode next;
  

• ListNode(int x) { val = x; }
  

• }
  */

class Solution {
public ListNode mergeKLists(ListNode[] lists) {
//分
int len=lists.length;
return mergeLists(lists,0,len-1);
}

    public static ListNode mergeLists(ListNode[] lists,int i,int j){
       if(i<j){
           int mid=(i+j)/2;
           ListNode left=mergeLists(lists,i,mid);
           ListNode right=mergeLists(lists,mid+1,j);
           return merge(left,right);
       }
       if(i==j){
           return lists[i];
       }

       return null;
       
    }

//和
public static ListNode merge(ListNode l1,ListNode l2){
if (l1 == null) return l2;
if (l2 == null) return l1;
if (l1.val < l2.val) {
l1.next = merge(l1.next, l2);
return l1;
} else {
l2.next = merge(l1,l2.next);
return l2;
}

 }

}

代码2：

class Solution {
public ListNode mergeKLists(ListNode[] lists) {
if (lists == null || lists.length == 0) return null;
PriorityQueue queue = new PriorityQueue<>(lists.length, new Comparator() {
@Override
public int compare(ListNode o1, ListNode o2) {
if (o1.val < o2.val) return -1;
else if (o1.val == o2.val) return 0;
else return 1;
}
});
ListNode dummy = new ListNode(0);
ListNode p = dummy;
for (ListNode node : lists) {
if (node != null) queue.add(node);
}
while (!queue.isEmpty()) {
p.next = queue.poll();
p = p.next;
if (p.next != null) queue.add(p.next);
}
return dummy.next;
}
}