[LeetCode] Problem 22 - Generate Parentheses

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Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

For example, given n = 3, a solution set is:

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[
  "((()))",
  "(()())",
  "(())()",
  "()(())",
  "()()()"
]

Code

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public List<String> generateParenthesis(int n) {
    List<String> result = new ArrayList<>();

    generateParenthesisHelper(result, n, 0, 0, "");

    return result;
}

private void generateParenthesisHelper(List<String> result, int n, int open, int close, String str) {
    if (str.length() == 2 * n) {
        result.add(str);
        return;
    }

    if (close < open)
        generateParenthesisHelper(result, n, open, close + 1, str + ")");

    if (open < n)
        generateParenthesisHelper(result, n, open + 1, close, str + "(");
}