```
public ListNode sortList(ListNode head) {
if (head == null || head.next == null) {
return head;
}
int length = 0;
for (ListNode cur = head; cur != null; cur = cur.next) {
++length;
}
ListNode cur = head;
for (int i = 0; i < length / 2 - 1; ++i) {
cur = cur.next;
}
ListNode right = sortList(cur.next);
cur.next = null;
ListNode left = sortList(head);
head = new ListNode(0);
cur = head;
while (left != null && right != null) {
if (left.val <= right.val) {
cur.next = left;
left = left.next;
} else {
cur.next = right;
right = right.next;
}
cur = cur.next;
}
if (left != null) {
cur.next = left;
} else {
cur.next = right;
}
return head.next;
}
```

You can still use two pointer instead of using list length, it will reduce the constants. However, it's more easy and readable to use length of the list.