1614. Maximum Nesting Depth of the Parentheses

class Solution {
    func maxDepth(_ s: String) -> Int {
        var count = 0
        var max = 0
        var b = ""
        for char in s {
            if char == "(" {
                b.append(char)
                count += 1
            } else if char == ")" {
                if max < count {
                    max = count
                }
                if b.last == "(" {
                    b.removeLast()
                }
                count -= 1
            }
        }
        if b.isEmpty {
            return max
        }
        return 0
    }
}