Leetcode852. 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: 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 <= 104

• 0 <= arr[i] <= 106

• arr is guaranteed to be a mountain array.

Success

Details 

Runtime: 1 ms, faster than 15.14% of Java online submissions for Peak Index in a Mountain Array.

Memory Usage: 45.8 MB, less than 19.80% of Java online submissions for Peak Index in a Mountain Array.