You're playing battleships, but you keep forgetting which squares in the grid you've already selected! Write a program to help you keep track of which squares you've hit. Your program should read in coordinates, one per line. If you haven't tried that square before, your program should print out Hit . If you have tried those coordinates already, you should print out You've chosen that square already. Your program should run until a blank line is entered, and should work like this: