{"id":7511,"date":"2022-11-11T11:29:40","date_gmt":"2022-11-11T09:29:40","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=7511"},"modified":"2022-12-14T11:45:47","modified_gmt":"2022-12-14T09:45:47","slug":"11-nov-22","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/11-nov-22\/","title":{"rendered":"Posiciones de un car\u00e1cter en una cadena"},"content":{"rendered":"

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

\n   posiciones :: Char -> String -> [Int]\n<\/pre>\n
tal que posiciones x ys<\/code> es la lista de la posiciones del car\u00e1cter x<\/code> en la cadena ys<\/code>. Por ejemplo,<\/p>\n
\n   posiciones 'a' \"Salamamca\"   ==  [1,3,5,8]\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 Data.List (elemIndices)\nimport Test.QuickCheck\n\n-- 1\u00aa soluci\u00f3n\n-- ===========\n\nposiciones1 :: Char -> String -> [Int]\nposiciones1 x ys = [n | (y,n) <- zip ys [0..], y == x]\n\n-- 2\u00aa soluci\u00f3n\n-- ===========\n\nposiciones2 :: Char -> String -> [Int]\nposiciones2 x ys = aux x ys 0\n  where\n    aux _ [] _ = []\n    aux b (a:as) n | a == b    = n : aux b as (n+1)\n                   | otherwise = aux b as (n+1)\n\n-- 3\u00aa soluci\u00f3n\n-- ===========\n\nposiciones3 :: Char -> String -> [Int]\nposiciones3 = elemIndices\n\n-- Comprobaci\u00f3n de equivalencia\n-- ============================\n\n-- La propiedad es\nprop_posiciones :: Char -> String -> Bool\nprop_posiciones x ys =\n  all (== posiciones1 x ys)\n      [posiciones2 x ys,\n       posiciones3 x ys]\n\n-- La comprobaci\u00f3n es\n--    \u03bb> quickCheck prop_posiciones\n--    +++ OK, passed 100 tests.\n\n-- Comparaci\u00f3n de eficiencia\n-- =========================\n\n-- La comparaci\u00f3n es\n--    \u03bb> length (posiciones1 'a' (take (6*10^6) (cycle \"abc\")))\n--    2000000\n--    (2.48 secs, 1,680,591,672 bytes)\n--    \u03bb> length (posiciones2 'a' (take (6*10^6) (cycle \"abc\")))\n--    2000000\n--    (2.98 secs, 1,584,591,720 bytes)\n--    \u03bb> length (posiciones3 'a' (take (6*10^6) (cycle \"abc\")))\n--    2000000\n--    (0.11 secs, 496,591,600 bytes)\n<\/pre>\n
<\/a>
\nSoluciones en Python<\/b><\/p>\n
\nfrom sys import setrecursionlimit\nfrom timeit import Timer, default_timer\n\nfrom hypothesis import given\nfrom hypothesis import strategies as st\n\nsetrecursionlimit(10**6)\n\n# -- 1\u00aa soluci\u00f3n\n# -- ===========\n\ndef posiciones1(x: str, ys: str) -> list[int]:\n    return [n for (n, y) in enumerate(ys) if y == x]\n\n# -- 2\u00aa soluci\u00f3n\n# -- ===========\n\ndef posiciones2(x: str, ys: str) -> list[int]:\n    def aux(a: str, bs: str, n: int) -> list[int]:\n        if bs:\n            if a == bs[0]:\n                return [n] + aux(a, bs[1:], n + 1)\n            return aux(a, bs[1:], n + 1)\n        return []\n    return aux(x, ys, 0)\n\n# -- 3\u00aa soluci\u00f3n\n# -- ===========\n\ndef posiciones3(x: str, ys: str) -> list[int]:\n    r = []\n    for n, y in enumerate(ys):\n        if x == y:\n            r.append(n)\n    return r\n\n# La propiedad es\n@given(st.text(), st.text())\ndef test_posiciones(x: str, ys: str) -> None:\n    r = posiciones1(x, ys)\n    assert posiciones2(x, ys) == r\n    assert posiciones3(x, ys) == r\n\n# La comprobaci\u00f3n es\n#    src> poetry run pytest -q posiciones_de_un_caracter_en_una_cadena.py\n#    1 passed in 0.29s\n\n# Comparaci\u00f3n de eficiencia\n# =========================\n\ndef tiempo(e: str) -> None:\n    \"\"\"Tiempo (en segundos) de evaluar la expresi\u00f3n e.\"\"\"\n    t = Timer(e, \"\", default_timer, globals()).timeit(1)\n    print(f\"{t:0.2f} segundos\")\n\n# La comparaci\u00f3n es\n#    >>> tiempo('posiciones1(\"a\", \"abc\"*6000)')\n#    0.00 segundos\n#    >>> tiempo('posiciones2(\"a\", \"abc\"*6000)')\n#    0.06 segundos\n#    >>> tiempo('posiciones3(\"a\", \"abc\"*6000)')\n#    0.00 segundos\n#\n#    >>> tiempo('posiciones1(\"a\", \"abc\"*(2*10**7))')\n#    3.02 segundos\n#    >>> tiempo('posiciones3(\"a\", \"abc\"*(2*10**7))')\n#    3.47 segundos\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
Definir la funci\u00f3n posiciones :: Char -> String -> [Int] tal que posiciones x ys es la lista de la posiciones del car\u00e1cter x en la cadena ys. Por ejemplo, posiciones ‘a’ \u00abSalamamca\u00bb == [1,3,5,8] Soluciones A continuaci\u00f3n se muestran las soluciones en Haskell y las soluciones en Python. Soluciones en Haskell import Data.List (elemIndices)…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"footnotes":"","_jetpack_memberships_contains_paid_content":false},"categories":[581],"tags":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/7511"}],"collection":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/comments?post=7511"}],"version-history":[{"count":2,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/7511\/revisions"}],"predecessor-version":[{"id":7650,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/7511\/revisions\/7650"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=7511"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=7511"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=7511"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}