FWIW: I've used the built in "memoize" and had not problem. You can
view my solution at http://bitbucket.org/tebeka/euler-clj/src/tip/14.clj
On Oct 6, 10:46 pm, Jarl Haggerty <fictivela...@gmail.com> wrote:
> Problem 14 on project Euler is to find the number under 1,000,000 that
> is the start of the longest Collatz sequence. My solution is below,
> basically it uses a hash map to cache the lengths of collatz
> sequences. But when I get to 113383 the collatz function just bounces
> between the numbers 1, 2, and 4. Those numbers seem to be in the map
> but contains? just keeps returning false.
>
> (ns euler.problem14)
>
> (def lengths (atom {1 0}))
>
> (defn collatz [input]
> (loop [current input accum 0]
> (when (= input 113383) (println current accum (filter #(< % 10)
> (keys @lengths))))
> (if (contains? @lengths current)
> (do
> (swap! lengths #(assoc % input (+ accum (get % current))))
> (get @lengths input))
> (if (zero? (mod current 2))
> (recur (/ current 2) (inc accum))
> (recur (inc (* 3 current)) (inc accum))))))
>
> (time (println (last (sort-by #(second %) (for [x (range 1 1000000)]
> (do (println x) [x (collatz x)]))))))
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