852. Peak Index in a Mountain Array

    func peakIndexInMountainArray(_ nums: [Int]) -> Int {
        var start = 1
        var end = nums.count - 2

        while start + 1 < end{
            let mid = (start + end) / 2
            if nums[mid - 1] < nums[mid]{
                start = mid
            } else{
                end = mid
            }
        }
        if nums[start] < nums[end] { return end }
        return start
    }