avlb.attachsubtree(1,(avltree)this[0]);
avlb.attachsubtree(2,(avltree)this[1][0]);
//avla.attachsubtree(1,avlb);
//this=avla;
this.key=this[1].key;
this[0]=avlb;
this[1]=this[1][1];
//调整两个节点的高度