{"id":7230,"date":"2022-08-16T06:00:50","date_gmt":"2022-08-16T04:00:50","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=7230"},"modified":"2022-12-14T16:53:04","modified_gmt":"2022-12-14T14:53:04","slug":"el-primero-al-final","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/el-primero-al-final\/","title":{"rendered":"El primero al final"},"content":{"rendered":"

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

\n   rota1 :: [a] -> [a]\n<\/pre>\n
tal que (rota1 xs)<\/code> es la lista obtenida poniendo el primer elemento de xs<\/code> al final de la lista. Por ejemplo,<\/p>\n
\n   rota1 [3,2,5,7]  ==  [2,5,7,3]\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 soluci\u00f3n\n-- ===========\n\nrota1a :: [a] -> [a]\nrota1a [] = []\nrota1a xs = tail xs ++ [head xs]\n\n-- 2\u00aa soluci\u00f3n\n-- ===========\n\nrota1b :: [a] -> [a]\nrota1b []     = []\nrota1b (x:xs) = xs ++ [x]\n\n-- Comprobaci\u00f3n de equivalencia\n-- ============================\n\n-- La propiedad es\nprop_rota1 :: [Int] -> Bool\nprop_rota1 xs =\n  rota1a xs == rota1b xs\n\n-- La comprobaci\u00f3n es\n--    \u03bb> quickCheck prop_rota1\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 soluci\u00f3n\ndef rota1a(xs: list[A]) -> list[A]:\n    if xs == []:\n        return []\n    return xs[1:] + [xs[0]]\n\n# 2\u00aa soluci\u00f3n\ndef rota1b(xs: list[A]) -> list[A]:\n    if xs == []:\n        return []\n    ys = xs[1:]\n    ys.append(xs[0])\n    return ys\n\n# 3\u00aa soluci\u00f3n\ndef rota1c(xs: list[A]) -> list[A]:\n    if xs == []:\n        return []\n    y, *ys = xs\n    return ys + [y]\n\n# La equivalencia de las definiciones es\n@given(st.lists(st.integers()))\ndef test_rota1(xs: list[int]) -> None:\n    assert rota1a(xs) == rota1b(xs) == rota1c(xs)\n\n# La comprobaci\u00f3n es\n#    src> poetry run pytest -q el_primero_al_final.py\n#    1 passed in 0.20s\n<\/pre>\n
El c\u00f3digo se encuentra en GitHub<\/a>.<\/p>\n
Comentarios<\/b><\/p>\n