162. Find Peak Element

Medium (Trung bình) Python 🔗 Xem trên LeetCode

📋 Đề Bài

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.

💻 Lời Giải

Python 0162-find-peak-element.py 
class Solution:
    def findPeakElement(self, nums: List[int]) -> int:
        n = len(nums)
        if n == 1:
            return 0
        if n == 2:
            return 0 if nums[0] > nums[1] else 1
        l = 0
        r = n - 2
        ans = 0
        
        while l <= r:
            m = (l + r) // 2
            
            if nums[m] < nums[m + 1]:
                ans = m + 1
                l = m + 1
            else:
                r = m - 1
        
        return ans