pascal編程求樹的後續遍歷

A,B:string;

procedure calc(s1,s2:string);

var

p:longint;

begin

if length(s1)<=1 then begin write(s1);exit;end;

p:=pos(s1[1],s2);

calc(copy(s1,2,p-1),copy(s2,1,p-1));

calc(copy(s1,p+1,length(s1)-p),copy(s2,p+1,length(s2)-p));

write(s1[1]);

end;

begin

readln(A);

readln(B);

calc(B,A);

writeln;

end.