Back to Problems

Find Peak Element

Medium
Binary Search

A peak element is an element that is strictly greater than its neighbors.

Given a 0-indexed integer array nums, find a peak element, and return its index. If the array contains multiple peaks, return the index to any of the peaks.

You may imagine that nums[-1] = nums[n] = -infinity. In other words, an element is always considered to be strictly greater than a neighbor that is outside the array.

You must write an algorithm that runs in O(log n) time.

Example 1

Input: nums = [1,2,3,1]
Output: 2
Explanation: 3 is a peak element and your function should return the index number 2.

Example 2

Input: nums = [1,2,1,3,5,6,4]
Output: 5
Explanation: Your function can return either index number 1 where the peak element is 2, or index number 5 where the peak element is 6.

Constraints

  • •1 <= nums.length <= 1000
  • •-2^31 <= nums[i] <= 2^31 - 1
  • •nums[i] != nums[i + 1] for all valid i.
Show Hints (3)
Hint 1: Binary search works even though the array is not sorted because we are looking for any peak, not a specific value.
Hint 2: If nums[mid] < nums[mid + 1], a peak must exist on the right side (the values are increasing).
Hint 3: If nums[mid] > nums[mid + 1], a peak must exist on the left side or at mid (the values are decreasing).
Loading editor...

Test Results

Click "Run" to execute your code against test cases

AI Tutor

Socratic guidance - I'll ask questions, not give answers

AI Tutor
Hello! I'm your AI tutor, here to guide you through this problem using the Socratic method. I won't give you direct answers, but I'll ask questions and provide hints to help you discover the solution yourself. What's your first instinct when you look at this problem? What approach comes to mind?