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43 lines
766 B
Ruby
43 lines
766 B
Ruby
# @param {Integer} n
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# @return {Integer}
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def tribonacci(n)
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sequence = [0, 1, 1]
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if n < 3 then
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return sequence[n]
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end
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(3..n).each {
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sequence = sequence.drop(1) + [sequence.sum]
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}
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return sequence.last
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end
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RSpec.describe "tribonacci of " do
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it "0 is 0" do
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expect(tribonacci(0)).to eq(0)
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end
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it "1 is 1" do
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expect(tribonacci(1)).to eq(1)
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end
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it "2 is 1" do
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expect(tribonacci(2)).to eq(1)
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end
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it "3 is 2" do
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expect(tribonacci(3)).to eq(2)
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end
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it "4 is 4" do
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expect(tribonacci(4)).to eq(4)
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end
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it "5 is 7" do
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expect(tribonacci(5)).to eq(7)
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end
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it "25 is 1389537" do
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expect(tribonacci(25)).to eq(1389537)
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end
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end
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