{"id":364,"date":"2014-06-30T07:00:49","date_gmt":"2014-06-30T05:00:49","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=364"},"modified":"2021-04-25T17:09:00","modified_gmt":"2021-04-25T15:09:00","slug":"eliminacion-de-n-elementos","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/eliminacion-de-n-elementos\/","title":{"rendered":"Eliminaci\u00f3n de n elementos"},"content":{"rendered":"<h4>Enunciado<\/h4>\n<pre lang=\"text\">\n-- Definir la funci\u00f3n\n--    elimina :: Int -> [a] -> [[a]]\n-- tal que (elimina n xs) es la lista de las listas obtenidas eliminando\n-- n elementos de xs. Por ejemplo,\n--    elimina 0 \"abcd\"  ==  [\"abcd\"]\n--    elimina 1 \"abcd\"  ==  [\"abc\",\"abd\",\"acd\",\"bcd\"]\n--    elimina 2 \"abcd\"  ==  [\"ab\",\"ac\",\"ad\",\"bc\",\"bd\",\"cd\"]\n--    elimina 3 \"abcd\"  ==  [\"a\",\"b\",\"c\",\"d\"]\n--    elimina 4 \"abcd\"  ==  [\"\"]\n--    elimina 5 \"abcd\"  ==  []\n--    elimina 6 \"abcd\"  ==  []\n<\/pre>\n<h4>Soluciones<\/h4>\n<pre lang=\"haskell\">\n-- 1\u00aa soluci\u00f3n:\nelimina1 :: Int -> [a] -> [[a]]\nelimina1 0 xs     = [xs]\nelimina1 n []     = []\nelimina1 n (x:xs) = [x:ys | ys <- elimina1 n xs] ++ elimina1 (n-1) xs\n\n-- 2\u00aa soluci\u00f3n:\nelimina2 :: Int -> [a] -> [[a]]\nelimina2 n xs = [ys | ys <- subsequences xs, length ys == k]\n    where k = length xs - n\n<\/pre>\n<h4>Referencia<\/h4>\n<p>El ejercicio est\u00e1 basado en el <a href=\"http:\/\/bit.ly\/1pduDjS\">problema del 5 de junio de 2014<\/a> de <a href=\"https:\/\/twitter.com\/1HaskellADay\">1HaskellADay<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Enunciado &#8212; Definir la funci\u00f3n &#8212; elimina :: Int -> [a] -> [[a]] &#8212; tal que (elimina n xs) es la lista de las listas obtenidas eliminando &#8212; n elementos de xs. Por ejemplo, &#8212; elimina 0 \u00ababcd\u00bb == [\u00ababcd\u00bb] &#8212; elimina 1 \u00ababcd\u00bb == [\u00ababc\u00bb,\u00bbabd\u00bb,\u00bbacd\u00bb,\u00bbbcd\u00bb] &#8212; elimina 2 \u00ababcd\u00bb == [\u00abab\u00bb,\u00bbac\u00bb,\u00bbad\u00bb,\u00bbbc\u00bb,\u00bbbd\u00bb,\u00bbcd\u00bb] &#8212; elimina 3&#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":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/364"}],"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=364"}],"version-history":[{"count":9,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/364\/revisions"}],"predecessor-version":[{"id":677,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/364\/revisions\/677"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=364"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=364"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=364"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}