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leetcode23.java
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leetcode23.java
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/**
* 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 == 0)
return null;
return helper(lists,0,lists.length - 1);
}
private ListNode helper(ListNode[] lists, int start, int end){
if(start == end)
return lists[start];
else if(start < end){
int mid = start + (end - start) / 2;
ListNode left = helper(lists,start,mid);
ListNode right = helper(lists,mid+1,end);
return mergeTwoLists(left,right);
}
else
return null;
}
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if(l1 == null){
return l2;
}
if(l2 == null){
return l1;
}
ListNode mergeHead;
if(l1.val < l2.val){
mergeHead = l1;
mergeHead.next = mergeTwoLists(l1.next, l2);
}
else{
mergeHead = l2;
mergeHead.next = mergeTwoLists(l1, l2.next);
}
return mergeHead;
}
}