LeetCode 22 Merge k Sorted Lists

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

递归版

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { *         val = x; *         next = null; *     } * } */public class Solution {    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {    ListNode head=new ListNode(-1);        if(l1==null&&l2==null) return null;        ListNode pNode=head;        while(l1!=null||l2!=null){if(l1==null) {pNode.next=l2;return head.next;}if(l2==null){pNode.next=l1;return head.next;}            if(l1.val>l2.val){pNode.next=l2;l2=l2.next;            }else {pNode.next=l1;l1=l1.next;            }            pNode=pNode.next;                           }        return head.next;    }    public ListNode mergeKLists(List<ListNode> lists) {        if(lists.size()==0) return (ListNode) null;            if(lists.size()==1) return lists.get(0);    List<ListNode> tempList=new ArrayList<ListNode>();    for(int i=1;i<lists.size();i+=2){    ListNode tempNode=mergeTwoLists(lists.get(i),lists.get(i-1));    tempList.add(tempNode);    }    if(lists.size()%2!=0) tempList.add(lists.get(lists.size()-1));        return mergeKLists(tempList);       }}

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