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// @Title: 括号生成 (Generate Parentheses)
// @Author: 15816537946@163.com
// @Date: 2020-11-03 08:38:49
// @Runtime: 0 ms
// @Memory: 2.8 MB
func generateParenthesis(n int) []string {
	var ans []string
	var dfs func(string, int, int)
	dfs = func(s string, left, right int) {
		if left > right {
			return
		}
		if left == 0 && right == 0 {
			ans = append(ans, s)
		}
		if left > 0 {
			dfs(s+"(", left-1, right)
		}
		if right > 0 {
			dfs(s+")", left, right-1)
		}
	}

	dfs("", n, n)

	return ans
}