Algorithms—23.Merge k Sorted Lists

思路：分治思想，拆分成2个进行处理。

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */public class Solution {    public ListNode mergeKLists(ListNode[] lists) {    if (lists.length>2) {    ListNode[] l1=new ListNode[lists.length/2];    ListNode[] l2=new ListNode[lists.length-lists.length/2];    for (int i = 0; i < lists.length; i++) {if (i<lists.length/2) {l1[i]=lists[i];}else {l2[i-lists.length/2]=lists[i];}}return mergeTwoLists(mergeKLists(l1),mergeKLists(l2));}else if (lists.length==2){return mergeTwoLists(lists[0],lists[1]);}else if (lists.length==1){return lists[0];}else {return null;}    }    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {          if (l1==null) {              return l2;          }          if (l2==null) {              return l1;          }          ListNode l=null;          if (l1.val>l2.val) {              l=new ListNode(l2.val);              l.next=mergeTwoLists(l1,l2.next);          }else {              l=new ListNode(l1.val);              l.next=mergeTwoLists(l1.next,l2);          }          return l;      }  }

耗时：356ms，第一次测的时候是中下游，再测了次变成上游了。