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@keisukeYamagishi
Created February 9, 2020 16:06
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順列の計算式を記録
def pattern (items, pattern)
(fact 4) / (fact (items.count - pattern))
end
#階乗
def fact(n, a=1)
return a if n == 0
fact(n-1, n*a)
end
p pattern [1,2,3,4], 4
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