ATTENTION

treenode tn1=parnode(1);
treenode tn2=parnode(2);
int rank1=getrank(tn1);
int rank2=getrank(tn2);
if(up(tn1)==up(tn2)){
    if(rank1>rank2){
        setrank(tn1,rank2);
        setrank(tn2,rank1);
    }
    else{
        setrank(tn2,rank1);
        setrank(tn1,rank2);
    }
}
else{
    treenode temp=up(tn2);
    transfernode(tn2,up(tn1));
    transfernode(tn1,temp);
    setrank(tn1,rank2);
    setrank(tn2,rank1);
}