LeetCode 162. Find Peak Element

Description

https://leetcode.com/problems/find-peak-element/

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

Given an input array nums, where nums[i] ≠ nums[i+1], find a peak element and return its index.

The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.

You may imagine that nums[-1] = nums[n] = -∞.

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: 1 or 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.

Note:

Your solution should be in logarithmic complexity.

Explanation

Use binary search to find

Python Solution

class Solution:
    def findPeakElement(self, nums: List[int]) -> int:
        start = 0
        end = len(nums) - 1
        
        while start + 1 < end:
            mid = start + (end - start) // 2
            if nums[mid - 1] < nums[mid] and nums[mid] > nums[mid + 1]:
                return mid
            elif nums[mid - 1] > nums[mid]:
                end = mid
            elif nums[mid] < nums[mid + 1]:
                start = mid
                
        if nums[end] > nums[start]:
            return end
        
        return start
  • Time complexity: O(log(N)).
  • Space complexity: O(1).

One Thought to “LeetCode 162. Find Peak Element”

Leave a Reply

Your email address will not be published. Required fields are marked *