Alien Invasion

This jump of the broken time machine again instead of taking you home, takes you to a future where you find yourself stuck in an alien invasion. Aliens have $N$ spacecrafts (numbered from $0$ to $N-1$) to attack Earth and each spacecraft has a power $Pi$. You encounter a helpful alien explorer, named Chitti, who gives you an Alien Technology weapon. Your task here is to help humans destroy thes