148. Sort List

Posted 2020-10-11 鸵鸟

class Solution {
    public ListNode sortList(ListNode head) {
        if(head==null||head.next==null)
            return head;
        ListNode p=head,q=head;
        while(p.next!=null&&p.next.next!=null)
        {
            q=q.next;
            p=p.next.next;
        }
        ListNode l2=sortList(q.next);
        q.next=null;
        ListNode l1=sortList(head);
        return merge(l1,l2);
    }
    private ListNode merge(ListNode l1, ListNode l2){
        ListNode l=new ListNode(0);
        ListNode p=l;
        while(l1!=null||l2!=null)
        {
            if(l1!=null&l2!=null&&l1.val<l2.val||l2==null)
            {
                p.next=l1;
                l1=l1.next;
            }
            else
            {
                p.next=l2;
                l2=l2.next;
            }
            p=p.next;
        }
        return l.next;
    }
}