38 lines
1.0 KiB
Lua
38 lines
1.0 KiB
Lua
--calculates the nth fibonacci number. Breaks for negative or non-integer n.
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function fibs(n)
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return n < 2 and n or fibs(n - 1) + fibs(n - 2)
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end
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--more pedantic version, returns 0 for non-integer n
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function pfibs(n)
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if n ~= math.floor(n) then return 0
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elseif n < 0 then return pfibs(n + 2) - pfibs(n + 1)
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elseif n < 2 then return n
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else return pfibs(n - 1) + pfibs(n - 2)
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end
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end
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--tail-recursive
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function a(n,u,s) if n<2 then return u+s end return a(n-1,u+s,u) end
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function trfib(i) return a(i-1,1,0) end
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--table-recursive
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fib_n = setmetatable({1, 1}, {__index = function(z,n) return n<=0 and 0 or z[n-1] + z[n-2] end})
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--table-recursive done properly (values are actually saved into table; also the first element
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-- of Fibonacci sequence is 0, so the initial table should be {0, 1}).
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fib_n = setmetatable({0, 1}, {
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__index = function(t,n)
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if n <= 0 then return 0 end
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t[n] = t[n-1] + t[n-2]
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return t[n]
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end
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})
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--loop version
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function lfibs(n)
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local p0,p1=0,1
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for _=1,n do p0,p1 = p1,p0+p1 end
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return p0
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end
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