Index of peak element

Find the index of any peak element in an integer array.

arrays search peak

A peak element is an element that is strictly greater than its neighbors. For the first and last elements, only consider the single existing neighbor. Given a list of integers `arr`, implement `find_peak_index(arr)` that returns the index of **any** peak element. The input list will have at least one element. If multiple peaks exist, returning any valid peak index is acceptable.

Constraints

1 <= len(arr) <= 10^5, values are integers within Python's int range.

Example

>>> find_peak_index([1, 2, 3, 1])
2
>>> find_peak_index([1, 2, 1, 3, 5, 6, 4])
1
>>> find_peak_index([3, 2, 1])
0

10 points ~15 min

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Hints

A linear scan comparing each element to its neighbors is sufficient for this problem.

For edges, consider only the neighbor that exists.

If arr has length 1, the single element is a peak (index 0).

Test Results

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