21 lines
463 B
Plaintext
21 lines
463 B
Plaintext
find(L, n) := block([i: 1, j: length(L), k, p],
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if n < L[i] or n > L[j] then 0 else (
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while j - i > 0 do (
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k: quotient(i + j, 2),
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p: L[k],
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if n < p then j: k - 1 elseif n > p then i: k + 1 else i: j: k
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),
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if n = L[i] then i else 0
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)
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)$
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".."(a, b) := if a < b then makelist(i, i, a, b) else makelist(i, i, a, b, -1)$
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infix("..")$
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a: sublist(1 .. 1000, primep)$
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find(a, 27);
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0
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find(a, 421);
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82
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