I have a nested loop to find all possible combinations of numbers between 1 and x in groups of 4, where a < b < c < d.
A method is called as each group is discovered to do a simple equivalency test on the sum of those numbers.
The loop does work and produces expected output (1 set of numbers for this particular x), however it takes 12+ seconds to find this answer and another ~5 to test the remaining possibilities, which is definitely bad, considering the x values are < 1000.
I tried having the outer loop iterate a < x - 3 times, the b loop b < x - 2 times, down to d < x times which didn't make a noticeable difference.
What would be a better approach in changing this loop?
for (a = 1; a < x; a++) {
for (b = a + 1; b < x; b++) {
for (c = b + 1; c < x; c++) {
for (d = c + 1; d < x; d++) {
check(a, b, c, d);
}
}
}
}