921. Minimum Add to Make Parentheses Valid

[kevin373738]

  public func minAddToMakeValid(_ s: String) -> Int {
        var closeNeeded = 0    // Tracks unmatched ')'
        var openNeeded = 0
        for str in s {
            switch str {
            case "(":
                openNeeded += 1
            case ")":
                if openNeeded > 0 {
                    openNeeded -= 1
                } else {
                    closeNeeded += 1
                }
            default:
                break
            }
        }
        
        return openNeeded + closeNeeded
    }