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class Solution {
public:
    vector<string> ans;

    void dfs(string an, int left, int right) {
        if (left < 0 || left > right)
            return;
        if (left == 0 && right == 0) {
            ans.push_back(std::move(an));
            return;
        }
        dfs(an + '(', left - 1, right);
        dfs(an + ')', left, right);
    }

    vector<string> generateParenthesis(int n) {
        dfs("", n, n);
        return ans;
    }
};