Is Find the Peaks easy or hard?

Find the Peaks is classified as an Easy problem. It focuses on basic array traversal and conditional checks rather than advanced data structures or algorithms. Most candidates solve it with a straightforward O(n) single-pass approach.

Find the Peaks Python/Java solution

The Python or Java implementation performs a loop from index 1 to n-2 and checks the two neighbor conditions. If both comparisons are true, the index is appended to a result list. The logic is identical across languages and runs in O(n) time with O(1) extra space.

How to solve Find the Peaks in O(n)?

Traverse the array from index 1 to n-2 and compare each element with its neighbors. If mountain[i] > mountain[i-1] and mountain[i] > mountain[i+1], record the index as a peak. Since every element is processed once, the algorithm runs in O(n) time with constant extra space.

What is the best approach for Find the Peaks?

The best approach is a single-pass linear scan of the array. Iterate from index 1 to n-2 and check whether each element is greater than its immediate neighbors. This solution runs in O(n) time and uses O(1) extra space, making it optimal for the problem.

Is Find the Peaks asked at Google/Amazon/Meta?

Find the Peaks reflects a common array traversal pattern frequently used in technical interviews. Variants of peak-finding and local maximum problems have appeared in interviews at companies like Google, Amazon, and Meta, especially in entry-level or screening rounds.

What data structure is used in Find the Peaks?

The primary data structure is an array. The algorithm performs sequential traversal and simple neighbor comparisons. The result is typically stored in a dynamic list or array of indices representing the peak positions.

What is the time complexity of Find the Peaks?

The time complexity is O(n) because the algorithm scans the array exactly once. For each index, it performs only two comparisons with neighboring elements. The extra space complexity is O(1) excluding the output list.

Description Hints 1 Solution Video 6:11

2951. Find the Peaks

Easy75.5% acceptance3 companies

You are given a 0-indexed array mountain. Your task is to find all the peaks in the mountain array.

Return an array that consists of indices of peaks in the given array in any order.

Notes:

A peak is defined as an element that is strictly greater than its neighboring elements.
The first and last elements of the array are not a peak.

Example 1:

Input: mountain = [2,4,4]
Output: []
Explanation: mountain[0] and mountain[2] can not be a peak because they are first and last elements of the array.
mountain[1] also can not be a peak because it is not strictly greater than mountain[2].
So the answer is [].

Example 2:

Input: mountain = [1,4,3,8,5]
Output: [1,3]
Explanation: mountain[0] and mountain[4] can not be a peak because they are first and last elements of the array.
mountain[2] also can not be a peak because it is not strictly greater than mountain[3] and mountain[1].
But mountain [1] and mountain[3] are strictly greater than their neighboring elements.
So the answer is [1,3].

Constraints: