arraySymmCount.swift

func fetchCount(array: [Int], length: Int, symmetric: Bool) -> Int {
    var count = 0
    
    for index in array.indices where index + length < array.count {
        let subArray = array[index..<(index + length)]
        print("Sub-array \"\(subArray)\" is \(subArray.allEqual() == true ? "Symmetrical" : "Asymmetrical")")
        if symmetric == subArray.allEqual() {
            count = count + 1
        }
    }
    return count
}

extension ArraySlice where Element : Equatable {
    func allEqual() -> Bool {
        if let firstElem = first {
            return !dropFirst().contains { $0 != firstElem }
        }
        return true
    }
}

let array = [1,1,2,2,3,3,3,4,5,6,7]
let length = 2
let symmetric = true
print("Total \(symmetric == true ? "Symmetrical" : "Asymmetrical") count is \(fetchCount(array: array, length: length, symmetric: symmetric))")

//Output
//Sub-array "[1, 1]" is Symmetrical
//Sub-array "[1, 2]" is Asymmetrical
//Sub-array "[2, 2]" is Symmetrical
//Sub-array "[2, 3]" is Asymmetrical
//Sub-array "[3, 3]" is Symmetrical
//Sub-array "[3, 3]" is Symmetrical
//Sub-array "[3, 4]" is Asymmetrical
//Sub-array "[4, 5]" is Asymmetrical
//Sub-array "[5, 6]" is Asymmetrical
//Total Symmetrical count is 4