852. 山脉数组的峰顶索引

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