20. 有效的括号

    func isValid(s string) bool {
        bracketMap := map[string]string{
            "(": ")",
            "[": "]",
            "{": "}",
        }
        var stack []string
        for _, c := range s {
            cs := string(c)
            if cs == "(" || cs == "[" || cs == "{" {
                stack = append(stack, bracketMap[cs])
            } else {
                if len(stack) == 0 {
                    return false
                }
                popCS := stack[len(stack) - 1]
                if popCS != cs {
                    return false
                }
                stack = stack[:len(stack) - 1]
            }
        }
        return len(stack) == 0
    }