SOURCE

var generateParenthesis = function (n) {
    let left = 0, right = 0, ans = []
    const _generate = function (left, right, n, s) {
        if (left === n && right === n) {
            ans.push(s)
            return
        }
        if (left < n) _generate(left + 1, right, n, s + "(")
        if (left > right) _generate(left, right + 1, n, s + ")")
    }
    _generate(left, right, n, "")
    return ans
};
console.log(generateParenthesis(3));