162. Find Peak Element

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

Description

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.

Solution

class Solution:
    def findPeakElement(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        def findpeak(nums, left, right):
            if left==right:
                return left
            if left==right-1:
                return left if nums[left]>nums[right] else right
            mid = (left+right)//2
            if nums[mid] <= nums[left]:
                return findpeak(nums, left, mid-1)
            if nums[mid] <= nums[right]:
                return findpeak(nums, mid+1, right)
            l_peak = findpeak(nums, left, mid)
            if l_peak != mid:
                return l_peak
            r_peak = findpeak(nums, mid, right)
            if r_peak != mid:
                return r_peak
            return mid
        
        return findpeak(nums, 0, len(nums)-1)

用时 36 ms，超过 99.34% 的运行时间。