[LeetCode] 148. Sort List java

    /**148. Sort List      * @param head     * @return O(nlogn)给链表排序     */    public ListNode sortList(ListNode head) {        if (head == null || head.next == null)            return head;        ListNode slow = head;        ListNode fast = head;        ListNode pre = head;        while (fast != null && fast.next != null) {            pre = slow;            slow = slow.next;            fast = fast.next.next;        }        pre.next = null;        head = sortList(head);        slow = sortList(slow);        return mergeTwoLists(slow, head);       }

//能够有O(n lgn)时间复杂度的算法为，快速排序，堆排序，归并排序
//根据复杂度想到应该用merge sort方法
//beats 85.60%

利用slow和fast指针找到中点，之后将头和中间节点进行排序，将排序好的链表合并