Hi!

You write that you use nested for. That is a very inefficient way to do it. Suppose n is the size of the array, you would need O(n^2) compares. In your case it is ~7000000*7000000, which is very much.

The following algorithm would be much faster O(n) (or ~7000000*3):

  1. create a temporary hash
  2. add all elements of the first array to that hash; use the array-value as a key and 1 as a value
  3. pass through the second array; if the current value is already in the hash, increase its value by 2
  4. pass through the hash; if all values are 3, array1 is part of array2

Another idea could be to sort both arrays (the perl sort-function is more efficient than a "nested-for-(bubble-)sort") and then work on the sorted arrays.

HTH, Rata

PS.: please be aware that the algorithm above does not work if the first array contains some values more than once!
PPS.: and of course you can improve the algorithm by adding checks on "more than once" in step 3 - and aborting the rest of the loops then

In reply to Re: Searching first array in second array. by Ratazong
in thread Searching first array in second array. by paragkalra

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