22. 括号生成

22. 括号生成`

func generateParenthesis(n int) []string { 
	var ret []string 
	help("", n, n, &ret) 
	return ret 
} 
func help(s string, left, right int, ret* []string){ 
	if left==0 && right == 0 { 
		*ret = append(*ret, s) 
	} 
	if left <= right { 
		if left >0 { 
			help(s+"(", left-1, right, ret) 
		} 
		if right > 0{ 
			help(s +")", left, right-1, ret) 
			} 
	} 
}