public static void main(String[] args) {
// TODO Auto-generated method stub
SortList s = new SortList();
ListNode head = new ListNode(2);
head.next = new ListNode(1);
s.sortList(head);
}
public ListNode sortList(ListNode head) {
if (head == null) return null;
if (head.next == null) // very important, missing this will cause stack
// overflow
return head;
ListNode mid = findMid(head);
ListNode right = sortList(mid.next);
mid.next = null;
ListNode left = sortList(head);
head = merge(left, right);
return head;
}
private ListNode merge(ListNode h1, ListNode h2) {
ListNode dummy = new ListNode(-1);
ListNode head = dummy;
while (h1 != null && h2 != null) {
if (h1.val < h2.val) {
dummy.next = h1;
h1 = h1.next;
} else {
dummy.next = h2;
h2 = h2.next;
}
dummy = dummy.next;
}
if (h1 != null) dummy.next = h1;
if (h2 != null) dummy.next = h2;
return head.next;
}