UVA 536(p177)----Tree Recovery

varpost,st1,st2,st:ansistring;l:longint;procedure solve(pre,mid:ansistring);var i:integer;begin if (pre='') or (mid='') then exit; i:=pos(pre[1],mid); solve(copy(pre,2,i),copy(mid,1,i-1)); solve(copy(pre,i+1,length(pre)-i),copy(mid,i+1,length(mid)-i)); post:=post+pre[1];end;begin while(not eof)do  begin   readln(st);   post:='';   l:=pos(' ',st);   st1:=copy(st,1,l-1);   st2:=copy(st,l+1,length(st));   solve(st1,st2);   writeln(post);  end;end.

题目地址：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=477