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Peak Index in a Mountain Array

SambaNova Systems● MediumNEW GRADPHONE SCREENONSITE INTERVIEW

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Problem statement

A mountain array strictly increases to one peak and then strictly decreases. Return the zero-based index of its peak.

Function

peakIndexInMountainArray(arr: int[]) → int

Examples

Example 1

arr = [0,1,0]return = 1

The middle element is the peak.

Example 2

arr = [0,2,5,3,1]return = 2

The sequence changes slope at index two.

Example 3

arr = [-5,-2,4,3]return = 2

Negative values do not change the slope logic.

Constraints

3 <= arr.length <= 100000.
-10^9 <= arr[i] <= 10^9.
There is exactly one peak and it is not an endpoint.