The solution relies on the value of the check variable, which is updated in each iteration. If an opening bracket is found, check is incremented by 1. In the case of a closing bracket, check is decremented by 1.

The logic is that check should never be negative because that would imply that somewhere in the string, there are more closing brackets than opening ones. The condition for being unbalanced is satisfied and we don’t need to check further.

Another case is that after the loop finishes, the value of check would be 0 because the brackets match. If it’s not, the function simply returns False.