哈，今日又聽到一條看似"mission impossible"的問題。我想這題用英文會好理解一點：
There is a submarine which is located at some integer point on the real axis at the 0th second. It moves with uniform velocity k units / sec, where k is an integer (possibly negative). As the submarine is deep under the water, you cannot see it. Every second you are allowed to fire a missile at some integer point. Find a way to fire the missiles so that you are guaranteed to fire at the submarine.
