852. Peak Index in a Mountain Array - LeetCode Solution

class Solution:
    def peakIndexInMountainArray(self, A: List[int]) -> int:
        start = 0
        end = len(A) -1


        while start<= end:
            mid = (start+end)//2

            nxt = (mid+1)%len(A)

            if A[mid] > A[nxt]:
                return mid

            elif A[mid] < A[end] and A[mid] <= A[start]:
                end = mid-1
            else:
                start = mid+1