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	helper(vector<string> &ans, int n, int i, int j, string s) {
        if (i > n || j > n || j > i) {
            return;
        }
        if (i == n && j == n) {
            ans.push_back(s);
            return;
        }
        helper(ans, n, i+1, j, s+"(");
        helper(ans, n, i, j+1, s+")");
    }
    vector<string> generateParenthesis(int n) {
        vector<string> ans;
        helper(ans, n, 0, 0, "");
        return ans;
    }

prog.cpp:1:8: error: expected constructor, destructor, or type conversion before ‘(’ token
  helper(vector<string> &ans, int n, int i, int j, string s) {
        ^
prog.cpp:12:5: error: ‘vector’ does not name a type
     vector<string> generateParenthesis(int n) {
     ^~~~~~

Standard output is empty