[USACO07DEC]BuildingRoadsS题目描述FarmerJohnhadjustacquiredseveralnewfarms!Hewantstoconnectthefarmswithroadssothathecantravelfromanyfarmtoanyotherfarmviaasequenceofroads;roadsalreadyconnectsomeofthefarms.EachoftheN(1≤N≤1,000)farms(convenientlynumbered1…N)isrepresentedbyaposition(Xi,Yi)ontheplane(0≤Xi≤1,