852. Peak Index in a Mountain Array

Medium

30 Points

Array

Binary Search

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.

Examples

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.