How can I avoid redundant comparisons when checking rectangle overlaps in C#?

Can't you just start j with int j = i + 1 in inner loop? Then you also wouldn't need if (i != j).

In the case of i>j, buttons[j] and buttons[i] have already been compared. And if there is hasOverlap, there is no need to compare further.

Make sure all buttons are already added before you run your loop, then just start the inner loop at j=i+1.

When you compare, first remove a button from the List, and compare it to the others. Repeat until all the buttons are removed (or otherwise done). So, a "while" loop. You can also use "Rect.Intersect()" as another way for checking overlap.

also, since you want to know "if any buttons overlap" you can stop the comparisons on the first overlap found. You do this with a break or a return if this is neatly in its own function.