两个列表中的公共元素具有重复 [英] Common elements in two lists with duplicates
问题描述
(列表,向量,序列)中的常用元素。共同元素[1] [1]); [1]
(common-elements [1 2] [1 1]); [1]
(common-elements [11] [1 1 1]); [1 1]
这里是我目前有的:
(defn remove-first [elem coll]
(lazy-seq
(when-let [s(seq coll)]
(let [f(first s),r(rest s)]
(if(= elem f)
r
(cons f(remove-first elem r)))))))))
(defn common-elements [coll1 coll2]
(lazy-seq
(when(and(seq coll1)(seq coll2))
(let [f (first coll1)]
(if(some#{f} coll2)
(cons f(common-elements(rest coll1)
(remove-first f coll2)))
(common-elements(rest coll1)coll2))))
=http://www.4clojure.com/ =nofollowtitle =4clojure> 4clojure 告诉我,我很少写最惯用的或简洁的代码,所以我有兴趣了解是否有更好的方法。
这是我的实现。它使用映射和集合来保存中间数据,因此不像你的版本那样懒惰,但我认为它更可读,并且将具有更好的整体性能特性(你的版本有二次时间复杂性来实现公共元素的结果)。
(require'[clojure.set:as set])
(defn common-elements [& colls]
(let [freqs(map frequencies colls)]
(mapcat(fn [e](repeat(apply min(map#(%e)freqs))e))
/ intersection(map(comp set keys)freqs)))))
I want to find the common elements in two [lists, vectors, sequences] when there can be duplicates.
(common-elements [1] [1]) ; [1]
(common-elements [1 2] [1 1]) ; [1]
(common-elements [1 1] [1 1 1]) ; [1 1]
Here is what I currently have:
(defn remove-first [elem coll]
(lazy-seq
(when-let [s (seq coll)]
(let [f (first s), r (rest s)]
(if (= elem f)
r
(cons f (remove-first elem r)))))))
(defn common-elements [coll1 coll2]
(lazy-seq
(when (and (seq coll1) (seq coll2))
(let [f (first coll1)]
(if (some #{f} coll2)
(cons f (common-elements (rest coll1)
(remove-first f coll2)))
(common-elements (rest coll1) coll2)))))
My experience with 4clojure has shown me that I rarely write the most idiomatic or succinct code so I'm interested in finding out whether there is a better way of doing this.
Here's my implementation. It uses maps and sets to hold intermediate data, and thus is not lazy like your version, but I think it is more readable and will have better overall performance characteristics (your version has quadratic time complexity to realize the results from common-elements).
(require '[clojure.set :as set])
(defn common-elements [& colls]
(let [freqs (map frequencies colls)]
(mapcat (fn [e] (repeat (apply min (map #(% e) freqs)) e))
(apply set/intersection (map (comp set keys) freqs)))))
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