thanks mand On Friday, February 1, 2013 12:41:44 AM UTC-2, Zack Maril wrote: > > Take a look at this gist: > https://gist.github.com/4688693 > > It uses memoize to eek out a little bit more performance. > λ ~/Projects/experiments/collatz > lein run > Compiling collatz.core > [9 19] > "Elapsed time: 30.236 msecs" > [97 118] > "Elapsed time: 5.532 msecs" > [871 178] > "Elapsed time: 22.529 msecs" > [6171 261] > "Elapsed time: 114.061 msecs" > [77031 350] > "Elapsed time: 578.955 msecs" > [837799 524] > "Elapsed time: 3686.937 msecs" > [8400511 685] > "Elapsed time: 40478.64 msecs" > > On my machine it is usually significantly faster than when I run the > provided code: > λ ~/Projects/experiments/collatz > lein run > Compiling collatz.core > {:n 9, :count 19} > "Elapsed time: 22.024 msecs" > {:n 97, :count 118} > "Elapsed time: 6.838 msecs" > {:n 871, :count 178} > "Elapsed time: 56.313 msecs" > {:n 6171, :count 261} > "Elapsed time: 293.266 msecs" > {:n 77031, :count 350} > "Elapsed time: 962.113 msecs" > {:n 837799, :count 524} > "Elapsed time: 9529.107 msecs" > λ ~/Projects/experiments/collatz > lein run > Compiling collatz.core > {:n 9, :count 19} > "Elapsed time: 28.077 msecs" > {:n 97, :count 118} > "Elapsed time: 8.1 msecs" > {:n 871, :count 178} > "Elapsed time: 31.023 msecs" > {:n 6171, :count 261} > "Elapsed time: 144.956 msecs" > {:n 77031, :count 350} > "Elapsed time: 944.857 msecs" > {:n 837799, :count 524} > "Elapsed time: 10030.467 msecs" > {:n 8400511, :count 685} > "Elapsed time: 113490.494 msecs" > > Of course, there is a bunch of optimizations you can take mathematically: > http://en.wikipedia.org/wiki/Collatz_conjecture > -Zack > On Friday, February 1, 2013 4:29:53 AM UTC+4, Leandro Moreira wrote: >> >> The problem is known as Collatz Conjecture (also 3n + 1 conjecture). >> Basically given a n number then you apply the following rule. >> >> If n is even then n/2 otherwise 3 * n + 1, you keep applying this until you >> reach the number 1. >> For instance, starting with *n = 6*, one gets the sequence 6, 3, 10, 5, 16, >> 8, 4, 2, 1. (with *8 items*) >> >> Now the challenge tell the *n* with n descending from 1000000 to 1 and with >> the *greater number of items*. >> >> Then I did the program bellow (I'm very happy for feedback since I'm totally >> noobie to clj), but it takes forever, there is anyway to make it fast? >> >> (defn- apply-collatz-conjecture >> "Given n, it returns n/2 if it's even or n*3+1 if it's odd." >> [n] >> (if (even? n) >> (/ n 2) >> (+ (* 3 n) 1))) >> >> (defn- collatz-conjecture-seq >> "Given n, it returns the sequence of collatz-conjecture." >> [n] >> (loop [n n sequence []] >> (if (not= n 1) >> (recur (apply-collatz-conjecture n) (cons >> (apply-collatz-conjecture n) sequence)) >> (reverse sequence)))) >> >> (defn- collatz-conjecture-number-of-items >> "It returns a map with n and number of items on its collatz-conjecture >> sequence." >> [n] >> { :n n :count (count (collatz-conjecture-seq n)) } ) >> >> (defn- greater >> "Given x and y, it returns the element with greater count." >> [x y] >> (if (> (:count x) (:count y)) >> x >> y)) >> >> (defn n-with-more-items >> "Given n, it applies collatz-conjecture for the range 1..n >> and return the n with more items." >> [n] >> (reduce greater (pmap collatz-conjecture-number-of-items (range 1 n)))) >> >> >> The only thing I thought was use pmap but it didn't make it super fast. >> >> *Using only map* >> user=> (time (n-with-more-items 999999)) >> "Elapsed time: *21191.762883 msecs*" >> {:n 837799, :count 524} >> >> *Using pmap* >> user=> (time (n-with-more-items 999999)) >> "Elapsed time: *13230.919979 msecs*" >> {:n 837799, :count 524} >> >> Any thoughts on how can I apply parallelism to solve this (especially on >> my frustrate try of use map and reduce)? >> >
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