雅布设计公司关键词自动优化

这道题目是一道回溯题，特殊之处在于右括号选择时，右括号的当前数量必须少于左括号的数量 

class Solution {private List<String> result;private void generateParenthesis(int n, StringBuilder stringBuilder, int open, int close) {if (2*n == stringBuilder.length()) {result.add(stringBuilder.toString());}if (open < n) {stringBuilder.append('(');generateParenthesis(n, stringBuilder, open + 1, close);stringBuilder.deleteCharAt(stringBuilder.length() - 1);}if (close < open) {stringBuilder.append(')');generateParenthesis(n, stringBuilder, open, close + 1);stringBuilder.deleteCharAt(stringBuilder.length() - 1);}}public List<String> generateParenthesis(int n) {result = new ArrayList<>();generateParenthesis(n, new StringBuilder(), 0, 0);return result;}
}