[Linked list] Merge k sorted linked lists (merge sort) - Programmer Sought
It is equivalent to merging n ordered singly linked lists, and each singly linked list has a length of 1.
Add each singly linked list to the list, and then apply the merge sort function.
import java.util.*;
/*
* public class ListNode {
* int val;
* ListNode next = null;
* }
*/
public class Solution {
/**
*
* @param head ListNode类 the head node
* @return ListNode类
*/
public ListNode sortInList (ListNode head) {
// write code here
if(head==null)return null;
ArrayList<ListNode>list=new ArrayList<>();
ListNode p=head;
while(p!=null){
ListNode q=p.next;
p.next=null;
list.add(p);
p=q;
}
return mergeKLists(list);
}
public ListNode merge(ListNode l1,ListNode l2){
if(l1==null||l2==null){
return l1==null?l2:l1;
}
ListNode dummyNode=new ListNode(-1);
ListNode cur=dummyNode;
while(l1!=null&&l2!=null){
if(l1.val<l2.val){
cur.next=l1;
l1=l1.next;
}else{
cur.next=l2;
l2=l2.next;
}
cur=cur.next;
}
cur.next=(l1==null?l2:l1);
return dummyNode.next;
}
public ListNode mergeList(ArrayList<ListNode> lists,int L,int R){
if(L==R){
return lists.get(L);
}
if(L>R)return null;
int mid=L+((R-L)>>1);
return merge(mergeList(lists,L,mid),mergeList(lists,mid+1,R));
}
public ListNode mergeKLists(ArrayList<ListNode> lists) {
return mergeList(lists,0,lists.size()-1);
}
}