Given a string, return the minimal number of parenthesis reversals needed to make balanced parenthesis.
For example:
solve(")(") = 2 Because we need to reverse ")" to "(" and "(" to ")". These are 2 reversals.
solve("(((())") = 1 We need to reverse just one "(" parenthesis to make it balanced.
solve("(((") = -1 Not possible to form balanced parenthesis. Return -1.
Parenthesis will be either "(" or ")".
More examples in the test cases.