这是我的第一个自己ak的分治题目！！！好耶！！（骄傲脸

思路参考：148. 排序链表（归并排序）

/*** 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) {return dfs(lists, 0, lists.length - 1);}public ListNode dfs(ListNode[] lists, int head, int tail) {if (head > tail) return null;if (head == tail) return lists[head];int mid = (head + tail) / 2;ListNode node1 = dfs(lists, head, mid);ListNode node2 = dfs(lists, mid + 1, tail);ListNode node = merge(node1, node2);return node;}public ListNode merge(ListNode node1, ListNode node2) {ListNode node = new ListNode(0);ListNode temp = node, temp1 = node1, temp2 = node2;while (temp1 != null && temp2 != null) {if (temp1.val < temp2.val) {temp.next = temp1;temp1 = temp1.next;} else {temp.next = temp2;temp2 = temp2.next;}temp = temp.next;}if (temp1 != null) temp.next = temp1;if (temp2 != null) temp.next = temp2;return node.next;}
}