{"id":770,"date":"2014-12-04T06:00:41","date_gmt":"2014-12-04T04:00:41","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=770"},"modified":"2016-05-01T20:22:50","modified_gmt":"2016-05-01T18:22:50","slug":"llanuras-de-longitud-dada","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/llanuras-de-longitud-dada\/","title":{"rendered":"Llanuras de longitud dada"},"content":{"rendered":"<h4>Enunciado<\/h4>\n<pre lang=\"text\">\n-- Una llanura de longitud n de una lista xs es una sublista de xs\n-- formada por n elementos iguales.\n--\n-- Definir la funci\u00f3n\n--    llanuras :: Eq a => Int -> [a] -> [[a]]\n-- tal que (llanuras n xs) es la lista de las llanuras de xs que tienen\n-- n elementos como m\u00ednimo. Por ejemplo,\n--    llanuras 3 \"aabbbcddddffxffxx\"  ==  [\"bbb\",\"dddd\"]\n<\/pre>\n<h4>Soluciones<\/h4>\n<pre lang=\"haskell\">\nimport Data.List (group)\nimport Test.QuickCheck\n\n-- 1\u00aa definici\u00f3n (por comprensi\u00f3n):\nllanuras :: Eq a => Int -> [a] -> [[a]]\nllanuras n xs = [ys | ys <- group xs, length ys >= n] \n\n-- 2\u00aa definici\u00f3n (por recursi\u00f3n con takeWhile y dropWhile):\nllanuras2 :: Eq a => Int -> [a] -> [[a]]\nllanuras2 _ [] = []\nllanuras2 n xs@(x:_) \n    | length ys >= n = ys : llanuras2 n (dropWhile (x==) xs) \n    | otherwise      = llanuras2 n (dropWhile (x==) xs) \n    where ys = takeWhile (x==) xs\n\n-- 3\u00aa definici\u00f3n (por recursi\u00f3n con span):\nllanuras3 :: Eq a => Int -> [a] -> [[a]]\nllanuras3 _ [] = []\nllanuras3 n xs@(x:_) \n    | length ys >= n = ys : llanuras3 n zs\n    | otherwise      = llanuras3 n zs\n    where (ys,zs) = span (x==) xs\n\n-- 4\u00aa definici\u00f3n (por recursi\u00f3n con span):\nllanuras4 :: Eq a => Int -> [a] -> [[a]]\nllanuras4 n = aux where\n    aux [] = []\n    aux xs@(x:_) | length ys >= n = ys : llanuras4 n zs\n                 | otherwise      = llanuras4 n zs\n                 where (ys,zs) = span (x==) xs\n\n-- ---------------------------------------------------------------------\n-- \u00a7 Verificaci\u00f3n                                                     --\n-- ---------------------------------------------------------------------\n\n-- Las definiciones son equivalentes\nprop_equivalencia :: Int -> [Int] -> Bool\nprop_equivalencia n xs =\n    llanuras2 n xs == ys &&\n    llanuras3 n xs == ys\n    where ys = llanuras n xs\n\n-- La comprobaci\u00f3n es\n--    ghci> quickCheck prop_equivalencia\n--    +++ OK, passed 100 tests.\n<\/pre>\n<h4>Referencias<\/h4>\n<p>Est\u00e9 ejercicio est\u00e1 basado en el problema <a href=\"http:\/\/bit.ly\/1vohF5p\">Llanura de n\u00fameros iguales con longitud igual a n<\/a> propuesto <a href=\"http:\/\/www.solveet.com\">Solveet!<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Enunciado &#8212; Una llanura de longitud n de una lista xs es una sublista de xs &#8212; formada por n elementos iguales. &#8212; &#8212; Definir la funci\u00f3n &#8212; llanuras :: Eq a => Int -> [a] -> [[a]] &#8212; tal que (llanuras n xs) es la lista de las llanuras de xs que tienen &#8211;&#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":[5],"tags":[8,59,13,28,11,6,60,34],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/770"}],"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=770"}],"version-history":[{"count":5,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/770\/revisions"}],"predecessor-version":[{"id":872,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/770\/revisions\/872"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=770"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=770"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=770"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}