23 Merge N Sorted Lists

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复习一下这道题。我一直都是用merge sort解法做的。今天在搜索别的解法时，发现这个文章讲的非常好： http://bangbingsyb.blogspot.com/2014/11/leetcode-merge-k-sorted-lists.html. 我的解法应该是属于第三种， time complexity nklog(k)

public class Solution {    public ListNode mergeKLists(ListNode[] lists) {        if (lists == null || lists.length == 0) {            return null;        }        return MSort(lists, 0, lists.length - 1);    }    public ListNode MSort(ListNode[] lists, int start, int end) {        if (start < end) {            int mid = start + (end - start) / 2;            ListNode left = MSort(lists, start, mid);            ListNode right = MSort(lists, mid + 1, end);            return mergeTwoLists(left, right);        }        return lists[start];    }    public ListNode mergeTwoLists(ListNode left, ListNode right) {        if (left == null && right == null) {            return null;        } else if (left == null) {            return right;        } else if (right == null) {            return left;        }        ListNode dummy = new ListNode(0);        ListNode head = dummy;        while (left != null && right != null) {            if (left.val > right.val) {                head.next = right;                right = right.next;            } else {                head.next = left;                left = left.next;            }            head = head.next;        }        if (left != null) {            head.next = left;        } else if (right != null) {            head.next = right;        }        return dummy.next;    }}

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