852. peak index in mountain array

You are given an integer mountain array arr of length n where the values increase to a peak element and then decrease.

Return the index of the peak element.

Your task is to solve it in O(log(n)) time complexity.

solution

Basic modified binary search.

def peakIndexInMountainArray(self, arr: List[int]) -> int:
	n = len(arr)
	l, r = 1, n-2
	  
	while l <= r:
		m = (l+r)//2
	  
		if arr[m-1] < arr[m] > arr[m+1]:
			return m
		elif arr[m-1] < arr[m] < arr[m+1]:
			l = m+1
		else:
			r = m-1
	return -1