CODEWITHSUNDEEP
javaruby
FourScore
FourScore

Reputation: 171

Why is Ruby so much slower than Java?

I was working on the Project Euler problems, when I stumbled on this problem. I wrote a program that solves it correctly in Ruby on Rails (new to the language):

class Collatz
 def search
    counter = 0
    storage = 0
    amount = 0
    (1..1000000).each do |i| i += 1
      temp = i
      while temp != 1
        temp = temp & 1 == 1 ? 3 * temp + 1 : temp >> 1
        counter += 1
      end
      if counter > amount
        amount = counter
        storage = i
      end
      counter = 0
    end
    puts storage
  end
end

start = Time.now
collatz = Collatz.new
collatz.search
ending = Time.now
puts "Time: #{ending - start}"

I realized that it took a very long time, 15.185317 seconds to be exact. When I try Java, however, the time is much shorter:

public class Euler{

    private static void problem() {
        long a;
        int j;
        int max = 0;
        int maxnr = 0;
        for(int i = 1; i < 1000000; i++) {
            a = i;
            j = 1;
            while( a != 1 ) {
                a = ((a & 1) == 1) ? (3 * a + 1) : (a >> 1);
                j++;
            }
            if(j > max) {
                max = j;
                maxnr = i;
            }
        }
        System.out.println(maxnr);
    }

    public static void main(String[] args) {
        long ct = System.currentTimeMillis();
        problem();
        long nt = System.currentTimeMillis() - ct;
        System.out.println(nt);
}

In the end this program took 769 milliseconds. I am using RubyMine for Ruby and Intellij IDEA for Java. I can't seem to figure out why it takes so long, and I'm not sure if it is normal or not. The task doesn't seem too difficult, since I'm just looping.

Upvotes: 1

Views: 287

Answers (1)

wvdz
wvdz

Reputation: 16651

Your solution to this problem is quite poor. It involves doing an enormous amount of duplicate work. Apparantly, the JVM is a lot better at optimizing this redundant work than Ruby.

However, if you would write a proper solution, which explicitly uses previous work you will find that it won't matter if you run it on Ruby or Java. You can do this by using an array or a map to store previous results. This technique is also known as dynamic programming.

Upvotes: 3

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