Leetcode #636: Exclusive Time of Functions

func exclusiveTime(_ n: Int, _ logs: [String]) -> [Int] {
    var answer = Array(repeating: 0, count: n)
    var stack = [Int]()
    var pretime = 0
    for i in stride(from: 0, to: logs.count, by: 1) {
        let components = logs[i].components(separatedBy: ":")
        let function = Int(components[0])!
        let timestamp = Int(components[2])!
        if stack.isEmpty {
            stack.append(function)
            pretime = timestamp
        } else {
            if components[1] == "start" {
                let top = stack.last!
                answer[top] += (timestamp - pretime)
                pretime = timestamp
                stack.append(function)
            } else {
                let top = stack.removeLast()
                answer[top] += (timestamp - pretime + 1)
                pretime = timestamp + 1
            }
        }
    }
    return answer
}