LeetCode -- Merge k Sorted Lists

LeetCode -- Merge k Sorted Lists

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

 

Question: Merge k ordered linked lists and return an ordered linked list.

Idea: I have previously done the merge of two ordered linked lists, so I want to simplify the merge of k linked lists into the merge of two linked lists.

 

public ListNode mergeKLists(List
 
   lists){if(lists == null)return null;return mergeLists(lists,0,lists.size()-1);}public ListNode mergeLists(List
  
    lists,int start,int end) {if(start > end)return null;if(start==end)return lists.get(start);if(start+1 == end)return mergeTwoLists(lists.get(start),lists.get(end));int mid = (start+end)/2;return mergeTwoLists(mergeLists(lists,start,mid),mergeLists(lists,mid+1,end));}public ListNode mergeTwoLists(ListNode l1, ListNode l2) {ListNode p1 = l1, p2 = l2, dummy = new ListNode(-1), p = dummy;while (p1 != null && p2 != null) {if (p1.val <= p2.val) {p.next = p1;p1 = p1.next;} else {p.next = p2;p2 = p2.next;}p = p.next;}if (p1 != null)p.next = p1;if (p2 != null)p.next = p2;return dummy.next;}// Definition for singly-linked list.public class ListNode {int val;ListNode next;ListNode(int x) {val = x;next = null;}}