Leetcode每日一题2021/01/19

class Solution:
    def peakIndexInMountainArray(self, arr: List[int]) -> int:
        left, right = 0, len(arr)-1
        while(left <= right):               # [0, len(arr)-1]
            mid = left + (right - left)//2
            if(arr[mid] < arr[mid+1]):      # 上升趋势
                left = mid + 1
            elif(arr[mid-1] > arr[mid]):    # 下降趋势
                right = mid - 1
            elif(arr[mid-1] < arr[mid] > arr[mid+1]):
                return mid
        return -1