At first , I didn't ignore the branch which contain 0 apple . so
got wrong answer. then I ignore it , accepted. though it seems to be
done in this way obviously . But I can't hardly understand it ! I
think ignoring it is illogical !!!  The context said that you should
cut n-1-Q Branches , then remain Q Branches in order to cut off the
fewest apples . If a branch has 0 apple , cutting it can waste none
apples !!!!!  Why not cut it but protect it ???  the context didn't
said that we can't cut the branch with 0 apple , how does somebody
know that ??? and why do they do that ?  I feel quite puzzled !