DrawArc - need call

func drawArc(_ arr: [Int]){
    guard arr.count > 0 else { return }
    var l = 0
    var r = arr.count - 1

    // need to handle corner case
    if arr[l] == 1 && arr[r] == 1 {
        while l < arr.count && arr[l] == 1 {
            l += 1
        }
        if l == arr.count {   // all 1
            print("at \(0) length \(arr.count)")
            return
        }
        while r >= l && arr[r] == 1 {
            r -= 1
        }
        print("at \(r + 1) length \(arr.count - 1 - r + l)")
    }

    // l at first point to calc， r at last calc position
    while l <= r {
        if arr[l] == 1 {
            let start = l
            l += 1
            while l <= r && arr[l] == 1 {
                l += 1
            }
            print("at \(start) length \(l - start)")
        }
        l += 1
    }
}