0852. Peak Index in a Mountain Array

https://leetcode.com/problems/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

Example 4:

**Input:** arr = [3,4,5,1]
**Output:** 2

Example 5:

**Input:** arr = [24,69,100,99,79,78,67,36,26,19]
**Output:** 2

Constraints:

• 3 <= arr.length <= 104

• 0 <= arr[i] <= 106

• arr is guaranteed to be a mountain array.

Follow up: Finding the O(n) is straightforward, could you find an O(log(n)) solution?

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