Description Link to heading

162. Find Peak Element (Medium)

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] = -∞. 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
  • -2³¹ <= nums[i] <= 2³¹ - 1
  • nums[i] != nums[i + 1] for all valid i.

Solution Link to heading

We can use binary search to solve this problem. Binary search doesn’t require monotonicity, actually it only requires dichotomy.