Question

What is the neatest algorithm for that ? Can it be done without helping/static variable ?

Answer 1

Use two “for” loops. Assuming that you don’t need to compare elements against themselves, and you only need to test each pair one way around rather than both ways:

for (int i = 1; i < ints.length; ++i) {
    for (int j = 0; j < i; ++j) {
        match(ints[i], ints[j]);
    }
}

If you want all pairs both ways, just change j < i to j < ints.length. If you want pairs both ways, excluding self-comparisons, either add if (i != j) in the inner loop or else do one inner loop from 0 to i-1, and another from i+1 to ints.length.