This problem is really excellent. Though it is so hard :) I've got AC
and I proud of it! If you want to see my solution - dimanyes@mail.ru

An excellent problem?! I don't think so. An excellent problem should
NOT be strict at 250KB memory size.

And, in my program, I've declared an 600KB array, and nothing else.
like:

Type
    Tdata    = array[1..LimitOpts] of
                  record
                      father         : word;
                      num            : longint;
                  end;

// LimitOpts = 100000


but, I've got Memory Limit Exceeded.

The program use about 350KB itself.

So you have use 350+600KB and It is MEMORY LIMIT.