[LeetCode] 23. 合并K个排序链表

一开始想到的方法一看官方解答好像很慢。。。。。

 看了精选答案：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
        if(lists==null||lists.length==0) return null;
        PriorityQueue<ListNode> queue=new PriorityQueue<>(lists.length, new Comparator<ListNode>() {
            @Override
            public int compare(ListNode o1, ListNode o2) {
                if(o1.val-o2.val<0)return -1;
                else if(o1.val==o2.val)return 0;
                else return 1;
            }
        });
        ListNode dummpy=new ListNode(0);
        ListNode p=dummpy;
        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 dummpy.next;
    }
}

 更快的是merge

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
        ListNode newHead = null;
        if(lists == null || lists.length == 0){
            return newHead;
        }
        int size = lists.length;
        if(size <= 1){
            return lists[0];
        }
        if(size <= 2){
            ListNode src1 = lists[0];
            ListNode src2 = lists[1];
            return mergeList(src1,src2);
        }else{
            int lengthLow = size / 2;
            int lengthHig = size - lengthLow;
            ListNode[] listLeft = new ListNode[lengthLow];
            ListNode[] listRigth = new ListNode[lengthHig];
            System.arraycopy(lists,0,listLeft,0,lengthLow);
            System.arraycopy(lists,lengthLow,listRigth,0,lengthHig);
            ListNode leftNode = mergeKLists(listLeft);
            ListNode rightNode = mergeKLists(listRigth);
            return mergeList(leftNode,rightNode);
        }
    }
    public ListNode mergeList(ListNode src1,ListNode src2){
        ListNode node = null;
        ListNode newHead = null;
        if(src1 == null){
                node = src2;
        }
        if(src2 == null){
            node = src1;
        }
        if(src1 == null || src2 == null){
            return node;
        }
        while(src1 != null && src2 != null){
            if(src1.val <= src2.val){
                if(node != null){
                    node.next = src1;
                    node = node.next;
                }else{
                    node = src1;
                    newHead = node;
                }
                src1 = src1.next;
            }else{
                if(node != null){
                    node.next = src2;
                    node = node.next;  
                }else{
                    node = src2;
                    newHead = node;
                }
                src2 = src2.next;
            }
            node.next= null;
        }
        if(src1 != null){
            node.next = src1;
        }
        if(src2 != null){
            node.next = src2;
        }
        return newHead;
    }
}