Leetcode #846: Hand of Straights

func isNStraightHand(_ hand: [Int], _ W: Int) -> Bool {
    if hand.count % W != 0 {
        return false
    }
    var dict = [Int: Int]()
    for num in hand {
        dict[num, default: 0] += 1
    }
    
    var sortedKey = dict.keys.sorted()
    while !sortedKey.isEmpty {
        let first = sortedKey[0]
        for i in stride(from: 0, to: W, by: 1) {
            if let value = dict[first+i] {
                dict[first+i] = value - 1
                if value == 1 {
                    if let index = sortedKey.firstIndex(of: first+i) {
                        sortedKey.remove(at: index)
                    }
                }
            } else {
                return false
            }
        }
    }
    return true
}