1021. Remove Outermost Parentheses
class Solution { public static String removeOuterParentheses(String S) { StringBuilder s = new StringBuilder(); int opened = 0; for (char c : S.toCharArray()) { if (c == '('&& opened > 0 ) s.append(c); if (c == ')'&& opened > 1) s.append(c); if (c == '(') opened++; else opened--; } return s.toString(); } }