Two comments:
  1. Your test is wrong: it does not check at all whether the least significant bit is set. Consider:
    • print 3 & 5; => 1
    • print 7 & 5; => 5
    In both of these tests the arguments have their LSB set, yet only the first test results in "1".

    The following tests the LSB of a variable: $value & 1

  2. Your inner loop is too long: if you know that both A and B have their significant bits set, then also B and A have their significant bits set By employing this symmetry you can eliminate half of your tests.
Update: Are you sure you want to have a hash with all the pairs of elements with the LSB set? This will quickly grow to enormous numbers: Assuming your integers are equally divided over odd and even numbers, the number of pairwise permutations will be 2000! (the factorial of 2000) which is larger than 10**499. Even if you can generate 1 million pairs per second, the program will run for more than 10**486 years.

Updated Update: Actually I was wrong: The number of permutations of subsets k drawn from a set of size n is n!/(n-k)! only, or in this case 2000! / 1998! or 2 000 * 1 999 = 3 998 000. Still a big number, but doable.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In reply to Re: Need a faster way to find matches by CountZero
in thread Need a faster way to find matches by remzak

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