{"id":3831,"date":"2018-03-05T07:00:54","date_gmt":"2018-03-05T05:00:54","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=3831"},"modified":"2018-03-12T09:07:41","modified_gmt":"2018-03-12T07:07:41","slug":"cruce-de-listas","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/cruce-de-listas\/","title":{"rendered":"Cruce de listas"},"content":{"rendered":"<p>Definir la funci\u00f3n<\/p>\n<pre lang=\"text\">\n   cruce :: Eq a => [a] -> [a] -> [[a]]\n<\/pre>\n<p>tal que (cruce xs ys) es la lista de las listas obtenidas uniendo las listas de xs sin un elemento con las de ys sin un elemento. Por ejemplo,<\/p>\n<pre lang=\"text\">\n   ghci> cruce [1,5,3] [2,4]\n   [[5,3,4],[5,3,2],[1,3,4],[1,3,2],[1,5,4],[1,5,2]]\n   ghci> cruce [1,5,3] [2,4,6]\n   [[5,3,4,6],[5,3,2,6],[5,3,2,4],[1,3,4,6],[1,3,2,6],\n    [1,3,2,4],[1,5,4,6],[1,5,2,6],[1,5,2,4]]\n<\/pre>\n<p>Comprobar con QuickCheck que el n\u00famero de elementos de (cruce xs ys) es el producto de los n\u00fameros de elementos de xs y de ys.<\/p>\n<h4>Soluciones<\/h4>\n<pre lang=\"haskell\">\nimport Data.List (delete)\nimport Test.QuickCheck\n\ncruce :: Eq a => [a] -> [a] -> [[a]]\ncruce xs ys = [(delete x xs) ++ (delete y ys) | x <- xs, y <- ys]\n\n-- La propiedad es\nprop_cruce :: Eq a => [a] -> [a] -> Bool\nprop_cruce xs ys =\n  length (cruce xs ys) == length xs * length ys\n\n-- La comprobaci\u00f3n es\n--    ghci> quickCheck prop_cruce\n--    +++ OK, passed 100 tests.\n<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>Definir la funci\u00f3n cruce :: Eq a => [a] -> [a] -> [[a]] tal que (cruce xs ys) es la lista de las listas obtenidas uniendo las listas de xs sin un elemento con las de ys sin un elemento. Por ejemplo, ghci> cruce [1,5,3] [2,4] [[5,3,4],[5,3,2],[1,3,4],[1,3,2],[1,5,4],[1,5,2]] ghci> cruce [1,5,3] [2,4,6] [[5,3,4,6],[5,3,2,6],[5,3,2,4],[1,3,4,6],[1,3,2,6], [1,3,2,4],[1,5,4,6],[1,5,2,6],[1,5,2,4]] Comprobar con&#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":[8,25,28,146],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/3831"}],"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=3831"}],"version-history":[{"count":2,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/3831\/revisions"}],"predecessor-version":[{"id":3858,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/3831\/revisions\/3858"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=3831"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=3831"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=3831"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}