/
combinatorics.cljc
20 lines (19 loc) · 940 Bytes
/
combinatorics.cljc
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(ns com.wsscode.common.combinatorics)
(defn cartesian-product
"All the ways to take one item from each sequence"
[& seqs]
(let [v-original-seqs (vec seqs)
step
(fn step [v-seqs]
(let [increment
(fn [v-seqs]
(loop [i (dec (count v-seqs)), v-seqs v-seqs]
(if (= i -1) nil
(if-let [rst (next (v-seqs i))]
(assoc v-seqs i rst)
(recur (dec i) (assoc v-seqs i (v-original-seqs i)))))))]
(when v-seqs
(cons (map first v-seqs)
(lazy-seq (step (increment v-seqs)))))))]
(when (every? seq seqs)
(lazy-seq (step v-original-seqs)))))