Binary Search. Θ(lgn)

///Binary Search Recursively. Θ(lgn)
func binarySearch<T: Comparable>(target:T, sortedArray: [T]) -> Int? {
    guard sortedArray.count > 0 else { return nil }
    return _binarySearch(target: target, sortedArray: sortedArray, low: 0, high: sortedArray.count-1)
}
func _binarySearch<T: Comparable>(target:T, sortedArray: [T], low:Int, high:Int) -> Int? {
    guard low != high else { return target==sortedArray[low] ? low : nil }
    let mid = (high+low)/2
    if sortedArray[mid] > target {
        return _binarySearch(target: target, sortedArray: sortedArray, low: low, high: mid)
    } else if sortedArray[mid] < target {
        return _binarySearch(target: target, sortedArray: sortedArray, low: mid+1, high: high)
    }
    return mid
}

///Binary Search Circularly. Θ(lgn)
func binarySearch<T: Comparable>(target:T, sortedArray: [T]) -> Int? {
    guard sortedArray.count > 0 else { return nil }
    var mid = 0, low = 0, high = sortedArray.count-1
    while low != high {
        mid = (high+low)/2
        if sortedArray[mid] == target { return mid }
        if sortedArray[mid] > target  { high = mid }
        else { low = mid+1 }
    }
    return target==sortedArray[low] ? low : nil
}

let r = try Int.random(above: 0, under: 99)
let s = Array(0...99)
binarySearch(target: r, sortedArray: s)