"""
Let's call an array A a mountain if the following properties hold:

A.length >= 3
There exists some 0 < i < A.length - 1 such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1]
Given an array that is definitely a mountain, return any i such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1].
"""

def peakIndexInMountainArray(self, A):
        lo, hi = 0, len(A) - 1
        while lo < hi:
            mi = (lo + hi) / 2
            if A[mi] < A[mi + 1]:
                lo = mi + 1
            else:
                hi = mi
            
        return hi