HTMLify

func valid(stack []rune) bool {
    var _s []rune
    for _, p := range stack {
        if p == '(' {
            _s = append(_s, p)
        } else {
            if  _s[len(_s)-1] == '(' {
                _s = _s[:len(_s)-1]
            }
        }
    }
    return len(_s) == 0
}
func removeOuterParentheses(s string) string {
    var stack []rune
    var ans string
    for _, p := range s {
        stack = append(stack, p)
        if valid(stack) {
            for _, _p := range stack[1:len(stack)-1] {
                ans += string(_p)
            }
            stack = nil
        }
    }
    return ans
}