leetcode 23. 合并K个排序链表 JAVA
题目:
合并 k 个排序链表,返回合并后的排序链表。请分析和描述算法的复杂度。
示例:
输入: [ 1->4->5, 1->3->4, 2->6 ] 输出: 1->1->2->3->4->4->5->6
解题思路:
使用归并将链表两两合并
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */ class Solution { public ListNode mergeKLists(ListNode[] lists) { if(lists.length == 1 ) return lists[0]; else if(lists == null) return null; return MSort(lists,0,lists.length - 1); } public ListNode MSort(ListNode[] lists, int low, int high){ if(low < high){ int mid = (low+high)/2; ListNode leftlist = MSort(lists,low,mid); ListNode rightlist = MSort(lists,mid+1,high); return mergeTwoLists(leftlist,rightlist); } else if(low == high) { return lists[low];// } else return null; // } public ListNode mergeTwoLists(ListNode l1, ListNode l2) { ListNode head = new ListNode(0); ListNode cur = head; ListNode p = l1, q = l2; while(p != null && q != null) { if(p.val <= q.val) { cur.next = new ListNode(p.val); cur = cur.next; p = p.next; } else { cur.next = new ListNode(q.val); cur = cur.next; q = q.next; } } while(p != null) { cur.next = new ListNode(p.val); cur = cur.next; p = p.next; } while(q != null) { cur.next = new ListNode(q.val); cur = cur.next; q = q.next; } return head.next; } }