Given a string of brackets, the task is to find an index k which decides the number of opening brackets is equal to the number of closing brackets. The string must consist of only opening and closing brackets.
"(())))("should return 4 since it splits the string into (()) and ))( and the number of ( in the former is equal to the number of ) in the latter.
"))" should return 2 since it splits the string into )) which has no ( in it and empty string which has no ) in it.