input: 確率 output: 当たりかどうか

hit.swift

func hit(percent: Float) -> Bool {
	let max = Int(100 / fabsf(percent))
	let value = Int.random(in: 1 ... max)
	return value == 1
}

test.swift

let percent: Float = 5 // 5%
let sum = (0..<10).map { _ -> Int in
	(0..<100).map { _ in hit(percent: percent) }.filter { $0 }.count
}.reduce(0, +)

let average: Float = Float(sum) / 10.0
print("平均: \(average)")