[Swiftアルゴリズム]ペアリングの削除

import Foundation

func solution(_ s:String) -> Int{
    if s.count % 2 == 0 {
        var stack = [Character]()
        for i in s {
            if stack.last == i {
                stack.removeLast()
            } else {
                stack.append(i)
            }
        }
        return stack.isEmpty ? 1 : 0
    }
    return 0
}