{"id":7262,"date":"2022-08-23T06:00:22","date_gmt":"2022-08-23T04:00:22","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=7262"},"modified":"2022-12-14T16:47:26","modified_gmt":"2022-12-14T14:47:26","slug":"elementos-finales","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/elementos-finales\/","title":{"rendered":"Elementos finales"},"content":{"rendered":"

Definir la funci\u00f3n<\/p>\n

\n   finales :: Int -> [a] -> [a]\n<\/pre>\n
tal que (finales n xs)<\/code> es la lista formada por los n<\/code> finales elementos de xs<\/code>. Por ejemplo,<\/p>\n
\n   finales 3 [2,5,4,7,9,6]  ==  [7,9,6]\n<\/pre>\n
Soluciones<\/b><\/p>\n
A continuaci\u00f3n se muestran las soluciones en Haskell<\/a> y las soluciones en Python<\/a>.<\/p>\n
<\/a>
\nSoluciones en Haskell<\/b><\/p>\n
\nimport Test.QuickCheck\n\n-- 1\u00aa definici\u00f3n\nfinales1 :: Int -> [a] -> [a]\nfinales1 n xs = drop (length xs - n) xs\n\n-- 2\u00aa definici\u00f3n\nfinales2 :: Int -> [a] -> [a]\nfinales2 n xs = reverse (take n (reverse xs))\n\n-- Comprobaci\u00f3n de equivalencia\n-- ============================\n\n-- La propiedad es\nprop_finales :: Int -> [Int] -> Bool\nprop_finales n xs =\n  finales1 n xs == finales2 n xs\n\n-- La comprobaci\u00f3n es\n--    \u03bb> quickCheck prop_finales\n--    +++ OK, passed 100 tests.\n<\/pre>\n
El c\u00f3digo se encuentra en GitHub<\/a><\/p>\n
<\/a>
\nSoluciones en Python<\/b><\/p>\n
\nfrom typing import TypeVar\nfrom hypothesis import given, strategies as st\n\nA = TypeVar('A')\n\n# 1\u00aa definici\u00f3n\ndef finales1(n: int, xs: list[A]) -> list[A]:\n    if len(xs) <= n:\n        return xs\n    return xs[len(xs) - n:]\n\n# 2\u00aa definici\u00f3n\ndef finales2(n: int, xs: list[A]) -> list[A]:\n    if n == 0:\n        return []\n    return xs[-n:]\n\n# 3\u00aa definici\u00f3n\ndef finales3(n: int, xs: list[A]) -> list[A]:\n    ys = list(reversed(xs))\n    return list(reversed(ys[:n]))\n\n# La propiedad de equivalencia es\n@given(st.integers(min_value=0), st.lists(st.integers()))\ndef test_equiv_finales(n, xs):\n    assert finales1(n, xs) == finales2(n, xs) == finales3(n, xs)\n\n# La comprobaci\u00f3n es\n#    src> poetry run pytest -q elementos_finales.py\n#    1 passed in 0.18s\n<\/pre>\n
El c\u00f3digo se encuentra en GitHub<\/a><\/p>\n
Comentarios<\/b><\/p>\n