{"id":6962,"date":"2022-04-20T09:37:09","date_gmt":"2022-04-20T07:37:09","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=6962"},"modified":"2022-04-30T16:22:10","modified_gmt":"2022-04-30T14:22:10","slug":"eliminacion-de-las-ocurrencias-aisladas","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/eliminacion-de-las-ocurrencias-aisladas\/","title":{"rendered":"Eliminaci\u00f3n de las ocurrencias aisladas."},"content":{"rendered":"<p>Definir la funci\u00f3n<\/p>\n<pre lang=\"text\">\n   eliminaAisladas :: Eq a => a -> [a] -> [a]\n<\/pre>\n<p>tal que <code>(eliminaAisladas x ys)<\/code> es la lista obtenida eliminando en <code>ys<\/code> las ocurrencias aisladas de <code>x<\/code> (es decir, aquellas ocurrencias de <code>x<\/code> tales que su elemento anterior y posterior son distintos de <code>x<\/code>). Por ejemplo,<\/p>\n<pre lang=\"text\">\n   eliminaAisladas 'X' \"\"                  == \"\"\n   eliminaAisladas 'X' \"X\"                 == \"\"\n   eliminaAisladas 'X' \"XX\"                == \"XX\"\n   eliminaAisladas 'X' \"XXX\"               == \"XXX\"\n   eliminaAisladas 'X' \"abcd\"              == \"abcd\"\n   eliminaAisladas 'X' \"Xabcd\"             == \"abcd\"\n   eliminaAisladas 'X' \"XXabcd\"            == \"XXabcd\"\n   eliminaAisladas 'X' \"XXXabcd\"           == \"XXXabcd\"\n   eliminaAisladas 'X' \"abcdX\"             == \"abcd\"\n   eliminaAisladas 'X' \"abcdXX\"            == \"abcdXX\"\n   eliminaAisladas 'X' \"abcdXXX\"           == \"abcdXXX\"\n   eliminaAisladas 'X' \"abXcd\"             == \"abcd\"\n   eliminaAisladas 'X' \"abXXcd\"            == \"abXXcd\"\n   eliminaAisladas 'X' \"abXXXcd\"           == \"abXXXcd\"\n   eliminaAisladas 'X' \"XabXcdX\"           == \"abcd\"\n   eliminaAisladas 'X' \"XXabXXcdXX\"        == \"XXabXXcdXX\"\n   eliminaAisladas 'X' \"XXXabXXXcdXXX\"     == \"XXXabXXXcdXXX\"\n   eliminaAisladas 'X' \"XabXXcdXeXXXfXx\"   == \"abXXcdeXXXfx\"\n<\/pre>\n<h4>Soluciones<\/h4>\n<pre lang=\"haskell\">\nmodule Elimina_aisladas where\n\nimport Data.List (group)\nimport Test.QuickCheck\n\n-- 1\u00aa soluci\u00f3n\n-- ===========\n\neliminaAisladas1 :: Eq a => a -> [a] -> [a]\neliminaAisladas1 _ [] = []\neliminaAisladas1 x [y]\n  | x == y    = []\n  | otherwise = [y]\neliminaAisladas1 x (y1:y2:ys)\n  | y1 \/= x   = y1 : eliminaAisladas1 x (y2:ys)\n  | y2 \/= x   = y2 : eliminaAisladas1 x ys\n  | otherwise = takeWhile (==x) (y1:y2:ys) ++\n                eliminaAisladas1 x (dropWhile (==x) ys)\n\n-- 2\u00aa soluci\u00f3n\n-- ===========\n\neliminaAisladas2 :: Eq a => a -> [a] -> [a]\neliminaAisladas2 _ [] = []\neliminaAisladas2 x ys\n  | cs == [x] = as ++ eliminaAisladas2 x ds\n  | otherwise = as ++ cs ++ eliminaAisladas2 x ds\n  where (as,bs) = span (\/=x) ys\n        (cs,ds) = span (==x) bs\n\n-- 3\u00aa soluci\u00f3n\n-- ===========\n\neliminaAisladas3 :: Eq a => a -> [a] -> [a]\neliminaAisladas3 x ys = concat [zs | zs <- group ys, zs \/= [x]]\n\n-- 4\u00aa soluci\u00f3n\n-- ===========\n\neliminaAisladas4 :: Eq a => a -> [a] -> [a]\neliminaAisladas4 x = concat . filter (\/= [x]) . group\n\n\n-- Comprobaci\u00f3n de equivalencia\n-- ============================\n\n-- La propiedad es\nprop_eliminaAisladas :: Int -> [Int] -> Bool\nprop_eliminaAisladas x ys =\n  all (== eliminaAisladas1 x ys)\n      [eliminaAisladas2 x ys,\n       eliminaAisladas3 x ys,\n       eliminaAisladas4 x ys]\n\n-- La comprobaci\u00f3n es\n--    \u03bb> quickCheck prop_eliminaAisladas\n--    +++ OK, passed 100 tests.\n\n-- Comparaci\u00f3n de eficiencia\n-- =========================\n\n-- La comparaci\u00f3n es\n--    \u03bb> length (eliminaAisladas1 'a' (take (5*10^6) (cycle \"abca\")))\n--    4999998\n--    (3.86 secs, 2,030,515,400 bytes)\n--    \u03bb> length (eliminaAisladas2 'a' (take (5*10^6) (cycle \"abca\")))\n--    4999998\n--    (3.41 secs, 2,210,516,832 bytes)\n--    \u03bb> length (eliminaAisladas3 'a' (take (5*10^6) (cycle \"abca\")))\n--    4999998\n--    (2.11 secs, 2,280,516,448 bytes)\n--    \u03bb> length (eliminaAisladas4 'a' (take (5*10^6) (cycle \"abca\")))\n--    4999998\n--    (0.92 secs, 1,920,516,704 bytes)\n<\/pre>\n<p>El c\u00f3digo se encuentra en <a href=\"https:\/\/github.com\/jaalonso\/Exercitium\/blob\/main\/src\/Elimina_aisladas.hs\">GitHub<\/a>.<\/p>\n<p>La elaboraci\u00f3n de las soluciones se describe en el siguiente v\u00eddeo<\/p>\n<p><iframe loading=\"lazy\" width=\"560\" height=\"315\" src=\"https:\/\/www.youtube.com\/embed\/7TJAdGjM3Ik\" title=\"YouTube video player\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture\" allowfullscreen><\/iframe><\/p>\n<h4>Nuevas soluciones<\/h4>\n<ul>\n<li>En los comentarios se pueden escribir nuevas soluciones.\n<li>El c\u00f3digo se debe escribir entre una l\u00ednea con &#60;pre lang=&quot;haskell&quot;&#62; y otra con &#60;\/pre&#62;\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Definir la funci\u00f3n eliminaAisladas :: Eq a => a -> [a] -> [a] tal que (eliminaAisladas x ys) es la lista obtenida eliminando en ys las ocurrencias aisladas de x (es decir, aquellas ocurrencias de x tales que su elemento anterior y posterior son distintos de x). Por ejemplo, eliminaAisladas &#8216;X&#8217; \u00ab\u00bb == \u00ab\u00bb eliminaAisladas&#8230;<\/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":[2],"tags":[41,8,12,498,59,38,13,11,6,60,34,146],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/6962"}],"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=6962"}],"version-history":[{"count":4,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/6962\/revisions"}],"predecessor-version":[{"id":6988,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/6962\/revisions\/6988"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=6962"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=6962"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=6962"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}