{"id":2939,"date":"2017-02-15T06:00:46","date_gmt":"2017-02-15T04:00:46","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=2939"},"modified":"2022-03-26T12:11:28","modified_gmt":"2022-03-26T10:11:28","slug":"busqueda-en-los-digitos-de-pi-2017","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/busqueda-en-los-digitos-de-pi-2017\/","title":{"rendered":"B\u00fasqueda en los d\u00edgitos de pi"},"content":{"rendered":"<p>El fichero <a href=\"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-content\/uploads\/2017\/02\/Digitos_de_pi.txt\">Digitos_de_pi.txt<\/a> contiene el n\u00famero pi con un mill\u00f3n de decimales; es decir,<\/p>\n<pre lang=\"text\">\n   3.1415926535897932384626433832 ... 83996346460422090106105779458151\n<\/pre>\n<p>Definir la funci\u00f3n<\/p>\n<pre lang=\"text\">\n   posicion :: String -> IO (Maybe Int)\n<\/pre>\n<p>tal que (posicion n) es (Just k) si k es la posici\u00f3n de n en la sucesi\u00f3n formada por un mill\u00f3n d\u00edgitos decimales del n\u00famero pi y Nothing si n no ocurre en dicha sucesi\u00f3n. Por ejemplo,<\/p>\n<pre lang=\"text\">\n   \u03bb> posicion \"15\"\n   Just 3\n   \u03bb> posicion \"2017\"\n   Just 8897\n   \u03bb> posicion \"022017\"\n   Just 382052\n   \u03bb> posicion \"14022017\"\n   Nothing\n   \u03bb> posicion \"999999\"\n   Just 762\n   \u03bb> posicion \"458151\"\n   Just 999995\n<\/pre>\n<p>Nota. Se puede comprobar la funci\u00f3n mediante <a href=\"http:\/\/www.angio.net\/pi\/piquery.html\">The pi-search page<\/a> o <a href=\"http:\/\/www.subidiom.com\/pi\">Pi search engine<\/a>.<\/p>\n<h4>Soluciones<\/h4>\n<pre lang=\"haskell\">\nimport Data.List (isPrefixOf)\n\nposicion :: String -> IO (Maybe Int)\nposicion ns = do\n  ds <- readFile \"Digitos_de_pi.txt\"\n  return (posicionEnLista (drop 2 ds) ns)\n\nposicionEnLista :: Eq a => [a] -> [a] -> Maybe Int\nposicionEnLista xs ys = aux xs 1\n  where aux [] _ = Nothing\n        aux (x:xs) n | ys `isPrefixOf` (x:xs) = Just n\n                     | otherwise              = aux xs (n+1)\n<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>El fichero Digitos_de_pi.txt contiene el n\u00famero pi con un mill\u00f3n de decimales; es decir, 3.1415926535897932384626433832 &#8230; 83996346460422090106105779458151 Definir la funci\u00f3n posicion :: String -> IO (Maybe Int) tal que (posicion n) es (Just k) si k es la posici\u00f3n de n en la sucesi\u00f3n formada por un mill\u00f3n d\u00edgitos decimales del n\u00famero pi y Nothing&#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":[4],"tags":[500,46,369,373,170,370,6,371,75],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/2939"}],"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=2939"}],"version-history":[{"count":5,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/2939\/revisions"}],"predecessor-version":[{"id":3008,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/2939\/revisions\/3008"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=2939"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=2939"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=2939"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}