0852-Peak-Index-In-A-Mountain-Array.py

'''
https://leetcode.com/problems/peak-index-in-a-mountain-array/

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

arr.length >= 3
There exists some i with 0 < i < arr.length - 1 such that:
- arr[0] < arr[1] < ... arr[i-1] < arr[i]
- arr[i] > arr[i+1] > ... > arr[arr.length - 1]
Given an integer array arr that is guaranteed to be a mountain,
return any i such that arr[0] < arr[1] < ... arr[i - 1] < arr[i] > arr[i + 1] > ... > arr[arr.length - 1].

Example 1:
Input: [0,1,0]
Output: 1

Example 2:
Input: [0,2,1,0]
Output: 1

Note:
3 <= A.length <= 10000
0 <= A[i] <= 10^6
A is a mountain, as defined above.
'''

# Method 1

class Solution:
    def peakIndexInMountainArray(self, arr: List[int]) -> int:
        start, end = 0, len(arr) - 1
        while start < end:
            mid = (start + end) // 2
            if arr[mid] > arr[mid + 1]:
                end = mid
            else:
                start = mid + 1
        return start

# Method 2

class Solution:
    def peakIndexInMountainArray(self, arr: List[int]) -> int:
        start, end = 0, len(arr) - 1
        while start <= end:
            mid = (start + end) // 2
            if arr[mid - 1] < arr[mid] > arr[mid + 1]:
                return mid
            elif arr[mid - 1] < arr[mid]:
                start = mid
            else:
                end = mid