BinarySearch.swift

let arr = (0...15).map {$0*2}

func binarySearch<T : Comparable>(arr : Array<T>, value : T) -> Bool {
    
    let midPosition = arr.startIndex.advancedBy(arr.startIndex.distanceTo(arr.endIndex)/2)
    let midElement = arr[midPosition]
    
    guard midElement != value else {
        return true
    }
    
    guard value >= arr[arr.startIndex] && value <= arr[arr.endIndex-1] else {
        return false
    }
    
    var subArray : Array<T>
    if value < midElement {
        subArray = Array(arr[arr.startIndex..<midPosition])
    } else {
        subArray = Array(arr[midPosition.successor()...arr.endIndex-1])
    }
    
    return binarySearch(subArray, value: value)
}

binarySearch(arr, value: 4) //True
binarySearch(arr, value:50323) //False