（准备写）URAL1824 Ifrit Bomber 题解

1824. Ifrit Bomber

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In the six years that passed since the
first experimental genie bombardments, Pitirim Schwartz has made
considerable advance. His latest invention is an ifrit bottle, which has
been developed especially for bombing large cities. Each ifrit from such a
bottle ruins everything within a radius of r miles from the
impact point. Only a few ifrit bottles are needed to demolish all
n large cities of a neighboring country… Alas, Pitirim has very
few ifrit bottles, so he has asked programmer Privalov to compute the
minimal number of bottles needed for the destruction of all the
cities.

For the convenience of aiming, the bottles
can only be dropped exactly on cities. The radius of destruction is so
large that cities can be regarded as points of the plane. When an ifrit
bottle is dropped, any city within or on the border of the destruction
zone is demolished.