Question

Is there any easy way to check if two arrays contain any common elements?
Is this appropriate? The arrays contain type char.

Arrays.asList(encryptU).contains(Ualpha[randNum]));

thanks in advance!

Answer 1

If the arrays are small, then a solution with a nested for loop (e.g. @scaryrawr’s) is going to perform best.

If the arrays are large enough, then the O(N^2) complexity of the above solution will be problematic. The solution is to use a HashSet; e.g.

HashSet<Character> tmp = new HashSet<Character>();
for (char ch : arr1) {
    tmp.add(ch);
}
for (char ch : arr2) {
    if (tmp.contains(ch)) {
        // elements in common!!
    }
}

This is O(N) in time, though the constant of proportionality is rather large. (I think you’d need the product of the array sizes to be 20 or 30 for this to be faster than the nested loop solution … but that is a guess.) Also, this requires O(N) temporary space.

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If the range of the characters is limited, then you could use a BitSet instead of a HashSet. That will also be roughly O(N) in time and space, though the range of the characters is also a factor in the complexity, so calling it O(N) is an over-simplification.

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But we are probably “over-thinking” this. The best advice would probably be to implement something simple, and if there is a suspicion that performance is a real concern then profile it to avoid wasting your time with unnecessary optimizing.