23. 合并K个排序链表
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
/** * 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 == null || lists.length == 0){ return null; } //每次合并两条 int len = lists.length; while(len != 1){ int i; for(i = 0;i < len / 2;i++){ lists[i] = merge2(lists[2 * i],lists[2 * i + 1]); } if(len % 2 == 1){ lists[i] = lists[len - 1]; len++; } len /= 2; } return lists[0]; } private ListNode merge2(ListNode l1,ListNode l2){ if(l1 == null && l2 == null) return null; ListNode dummy = new ListNode(-1); ListNode pre = dummy; while(l1 != null && l2 != null){ if(l1.val < l2.val){ pre.next = l1; l1 = l1.next; }else{ pre.next = l2; l2 = l2.next; } //更新pre pre = pre.next; } pre.next = (l1 == null) ? l2 : l1; return dummy.next; } }
一回生,二回熟