class Solution {
    func nextClosestTime(_ time: String) -> String {
        var cur = 60 * Int(time.prefix(2))!
        cur += Int(time.suffix(2))!
        var allowed = Set(time.filter { $0 != ":" }.map { $0.wholeNumberValue! })

        while true {
            cur = (cur + 1) % (24 * 60)
            let digits = [cur / 60 / 10, cur / 60 % 10, cur % 60 / 10, cur % 60 % 10]
            if digits.allSatisfy({ allowed.contains($0) }) {
                return String(format: "%02d:%02d", cur / 60, cur % 60)
            }
        }
    }
}