leetcode 707

        if(index==0){
            addAtHead(val);
            return;
        }
        while(p!=null&&i<index-1){
            p = p.next;
            i++;
        }
        if(p!=null){
            node.next = p.next;
            p.next = node;
        }
    }

    public void deleteAtIndex(int index) {
        ListNode dummyNode = new ListNode();
        dummyNode.next = head;
        ListNode p = dummyNode;
        int i = 0;
        if(index==0){
            head = head.next;
        }
        while(p.next!=null&&i<index){
            p = p.next;
            i++;
        }
        if(p.next!=null){
            p.next = p.next.next;
        }
    }

    public void show(ListNode list){
        ListNode p = list;
        while(p!=null){
            System.out.print(p.val+" ");
            p = p.next;
        }
        System.out.println();
    }

    class ListNode {
        public int val;
        public ListNode next;
        public ListNode() {
        }
        ListNode(int val) {
            this.val = val;
        }
        public ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }
}