class Solution {
public ListNode sortList(ListNode head) {
if (head == null || head.next == null)
return head;
ListNode prev = null;
ListNode slow = head;
ListNode fast = head;
while (fast != null && fast.next != null ) {
prev = slow;
slow = slow.next;
fast = fast.next.next;
}
prev.next = null;//将前半段链表设置为null结尾，链表被分成(head,p),(slow,fast)
ListNode l1 = sortList(head);
ListNode l2 = sortList(slow);
return merge(l1, l2);
}
private ListNode merge(ListNode l1, ListNode l2) {
ListNode l = new ListNode(0);//设置辅助节点
ListNode p = l;
while (l1 != null && l2 != null) {
if (l1.val < l2.val) {
p.next = l1;
l1 = l1.next;
} else {
p.next = l2;
l2 = l2.next;
}
p = p.next;//要把p向前移动
}
if (l1 != null)
p.next = l1;
if (l2 != null)
p.next = l2;
return l.next;
}
}
