Peak Index in a Mountain Array
Difficulty: Medium
Category: DSA
Topics: Array, Binary Search
Asked at: Bloomberg, Yahoo
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.
**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
**Constraints:**
- `3 <= arr.length <= 105`
- `0 <= arr[i] <= 106`
- `arr` is **guaranteed** to be a mountain array.