비내림차순 배열에서의 upperBound&lowerBound 구현

upper&lowerBound.swift

extension Array where Element: Comparable {
    func lowerBound(of element: Element) -> Int {
        var left = startIndex
        var right = count

        while left < right {
            let mid = (left+right)/2

            if self[mid] >= element {
                right = mid
            } else {
                left = mid+1
            }
        }

        return right
    }

    func upperBound(of element: Element) -> Int {
        var left = startIndex
        var right = count

        while left < right {
            let mid = (left+right)/2

            if self[mid] <= element {
                left = mid+1
            } else { right = mid }
        }

        return right
    }
}