4clojure 题解 Set Intersection

求两个set的交集合，不允许使用Intersection

Write a function which returns the intersection of two sets. The intersection is the sub-set of items that each set has in common.

	(= (__ #{0 1 2 3} #{2 3 4 5}) #{2 3})
	(= (__ #{0 1 2} #{3 4 5}) #{})
	(= (__ #{:a :b :c :d} #{:c :e :a :f :d}) #{:a :c :d})

参考了clojure.set/intersection 的实现

(fn [s1 s2]
   (reduce (fn [result item]
             (if (contains? s2 item)
               result
               (disj result item))
             ) s1 s1)
   )

disj 是一个从集合中去除指定项目返回一个新集合的操作