{"id":1564,"date":"2015-06-16T06:00:22","date_gmt":"2015-06-16T04:00:22","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=1564"},"modified":"2015-10-28T15:17:51","modified_gmt":"2015-10-28T13:17:51","slug":"suma-de-posteriores","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/suma-de-posteriores\/","title":{"rendered":"Suma de posteriores"},"content":{"rendered":"<p>Definir la funci\u00f3n<\/p>\n<pre lang=\"text\">\n   sumaPosteriores :: [Int] -> [Int]\n<\/pre>\n<p>tal que (sumaPosteriores xs) es la lista obtenida sustituyendo cada elemento de xs por la suma de los elementos posteriores. Por ejemplo,<\/p>\n<pre lang=\"text\">\n   sumaPosteriores [1..8]        == [35,33,30,26,21,15,8,0]\n   sumaPosteriores [1,-3,2,5,-8] == [-4,-1,-3,-8,0]\n<\/pre>\n<p>Comprobar con QuickCheck que el \u00faltimo elemento de la lista (sumaPosteriores xs) siempre es 0.<\/p>\n<h4>Soluciones<\/h4>\n<pre lang=\"haskell\">\nimport Data.List (tails)\nimport Test.QuickCheck\n\n-- 1\u00aa definici\u00f3n (por recursi\u00f3n):\nsumaPosteriores1 :: [Int] -> [Int]\nsumaPosteriores1 []     = []\nsumaPosteriores1 (x:xs) = sum xs : sumaPosteriores1 xs\n\n-- 2\u00aa definici\u00f3n (sin argumentos)\nsumaPosteriores2 :: [Int] -> [Int]\nsumaPosteriores2 = map (sum . tail) . init . tails\n\n-- La propiedad es\npropSumaP:: [Int] -> Property\npropSumaP xs = not (null xs) ==> last (sumaPosteriores1 xs) == 0\n\n-- La comprobaci\u00f3n es\n--    ghci> quickCheck propSumaP\n--    +++ OK, passed 100 tests.\n<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>Definir la funci\u00f3n sumaPosteriores :: [Int] -> [Int] tal que (sumaPosteriores xs) es la lista obtenida sustituyendo cada elemento de xs por la suma de los elementos posteriores. Por ejemplo, sumaPosteriores [1..8] == [35,33,30,26,21,15,8,0] sumaPosteriores [1,-3,2,5,-8] == [-4,-1,-3,-8,0] Comprobar con QuickCheck que el \u00faltimo elemento de la lista (sumaPosteriores xs) siempre es 0. Soluciones import&#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":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/1564"}],"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=1564"}],"version-history":[{"count":2,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/1564\/revisions"}],"predecessor-version":[{"id":1649,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/1564\/revisions\/1649"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=1564"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=1564"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=1564"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}