Question

TL DR; What is the most efficient way to sort and compare values in a multiple arrays?

Okay, so we’ll assume a few constants to make this whole thing simple
var a = [1, 2, 3, 4, 5, 6], b = [0, 9, 8, 7, 6, 88, 99, 77], i, j;

Now if I wanted to see if any value in a is equal to any other value in b I’d have to sort through one of these arrays 6 times. That’s a lot of work, and it would seem there should be a more efficient way to do this. For those needing a visual aide here you are ( and yes I know about — and ++ I just don’t like to use ’em ):

for (i = a.length - 1; i > -1; i -= 1) {
    for (j = b.length - 1; j > -1; j -= 1) {
        if (a[i] === b[j]) {
            return b[j];
        }
    }
}

The B array gets ran through once for EACH element in A. Again, certainly there is a more efficient way to complete this task?

-Akidi

Answer 1

Depends on the size of your input arrays (several tradeoffs there)– your nested loops are simplest for small inputs like your examples.

If you have huge arrays, and have control over their construction, consider keeping a map (Object in JS) around acting as a lookup set (if you’re creating a in a loop anyways, you can build the set in parallel.)

var setA = {};
for (int i = 0; i < a.length; i++) {
    setA[a[i]] = true;
}

Then you can see whether something exists in the set by just checking setA[?].

Likewise with B, or with both together, etc, depending on your needs.