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Leetcode
Medium
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Peak Index In A Mountain Array

Find the index of the peak element in a mountain array.

Acceptance 90%
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Problem Statement

Problem

You are given a mountain array arr of length n.

A mountain array has the following properties:

  • n >= 3
  • There exists an index peak such that:
    • arr[0] < arr[1] < ... < arr[peak]
    • arr[peak] > arr[peak + 1] > ... > arr[n - 1]

Your task is to return the index of the peak element.

A correct solution should be better than linear scan when possible and should work for the mountain structure described above.

Input Format

  • One integer array arr representing a mountain array.
  • The array has exactly one peak.

Output Format

  • Return a single integer: the index of the peak element.

Constraints

  • 3 <= arr.length
  • arr is guaranteed to be a mountain array
  • The peak is unique
  • Values in the array are integers
Examples
Sample cases returned by the problem API.

Example 1

Input

arr = [0, 2, 4, 3, 1]

Output

2

Explanation

The values increase up to 4 at index 2, then decrease afterward, so the peak index is 2.

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