swift 二分查找

给Array添加延展

extension Array where Element == Int {
    /// 二分查找：判断有序的数组里面是否包含某一个数字
    func binarySearch(x: Int) -> Bool {
        var result = false
        let min = self.startIndex
        let max = self.endIndex - 1

        if min > max {
            return false
        }

        let mid = Int((min + max)/2)
        let value = self[mid]

        if x == value {
            return true
        }

        if x < value {
            let array = min < mid ? Array(self[min..<mid]) : Array<Int>()
            result = array.binarySearch(x: x)
        }

        if x > value {
            let array = max > mid ? Array(self[mid..<max]) : Array<Int>()
            result = array.binarySearch(x: x)
        }
        return result
    }
}