用单位圆覆盖尽量多的点

This is the first time that I try to write my blog in English,so excuse me for the lanuage errors. Considering a problem like this:there are great quantities of points on the flat,and now use a circle of radius one to cover as many point as you can.Then how many points can you cover at most?
The algorithm to solve this Enumerate.If there is only one point on the flat then the answer should be one.Choose two points randomly,and calculate the center of the circle whose radius is one.Then go through all points and get the number of how many points are in the circle.So,the entent of time conplexity is O(n^3).