Algorithms in Swift

binary-search.swift

extension Array where Element: Comparable {
    func binarySearch(_ target: Element) -> Int? {
        var lower = 0
        var upper = count
        while lower < upper {
            let mid = lower + (upper - lower) / 2
            if self[mid] == target {
                return mid
            } else if self[mid] < target {
                lower = mid + 1
            } else {
                upper = mid
            }
        }

        return nil
    }
}

let numbers = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67]
print(numbers.binarySearch(100) ?? -1)