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62 lines
1.4 KiB
Clojure
62 lines
1.4 KiB
Clojure
(ns koans.14-recursion
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(:require [koan-engine.core :refer :all]))
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(defn is-even? [n]
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(if (= n 0)
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true
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(not (is-even? (dec n)))))
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(defn is-even-bigint? [n]
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(loop [n n
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acc true]
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(if (= n 0)
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acc
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(recur (dec n) (not acc)))))
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(defn recursive-reverse [coll]
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(if (empty? coll)
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coll
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(concat (recursive-reverse (rest coll)) (list (first coll)))))
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(defn factorial [n]
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(loop [n n
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acc 1]
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(if (= n 0)
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acc
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(recur (dec n) (* n acc)))
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))
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(meditations
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"Recursion ends with a base case"
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(= true (is-even? 0))
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"And starts by moving toward that base case"
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(= false (is-even? 1))
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"Having too many stack frames requires explicit tail calls with recur"
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(= false (is-even-bigint? 100003N))
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"Reversing directions is easy when you have not gone far"
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(= '(1) (recursive-reverse [1]))
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"Yet it becomes more difficult the more steps you take"
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(= '(6 5 4 3 2) (recursive-reverse [2 3 4 5 6]))
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"Simple things may appear simple."
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(= 1 (factorial 1))
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"They may require other simple steps."
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(= 2 (factorial 2))
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"Sometimes a slightly bigger step is necessary"
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(= 6 (factorial 3))
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"And eventually you must think harder"
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(= 24 (factorial 4))
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"You can even deal with very large numbers"
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(< 1000000000000000000000000N (factorial 1000N))
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"But what happens when the machine limits you?"
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(< 1000000000000000000000000N (factorial 100003N)))
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