0022.括号生成

func generateParenthesis(n int) []string {
	ans := []string{}
	var backtrack func(left, right int, seqence string)
	backtrack = func(left, right int, seqence string) {
		if left == 0 && right == 0 {
			ans = append(ans, seqence)
			return
		}
		if left > right || left < 0 || right < 0 {
			return
		}

		backtrack(left-1, right, seqence+"(")
		backtrack(left, right-1, seqence+")")
	}
	backtrack(n, n, "")
	return ans
}