[Leetcode]852. Peak Index in a Mountain Array

📄 Description

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: arr = [0,1,0]
Output: 1

Example 2:

Input: arr = [0,2,1,0]
Output: 1

Example 3:

Input: arr = [0,10,5,2]
Output: 1

🔨 My Solution

• use Binary Search Algorithm

💻 My Submission

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

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