162. Find Peak Element

Medium

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

Given an 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] = -∞.

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.

class Solution:
    def findPeakElement(self, nums: List[int]) -> int:
        if len(nums) == 1:
            return 0
        def findPeak(nums, low, high):
            if low > high:
                return -1
            mid= low+(high-low)//2
            if mid==0 and nums[mid] > nums[mid+1]:
                return mid
            elif mid == len(nums)-1 and nums[mid] > nums[mid-1]:
                return mid
            elif nums[mid-1] < nums[mid] > nums[mid+1]:
                return mid
            left = findPeak(nums, low, mid-1)
            if left == -1:
                return findPeak(nums, mid+1, high)
            return left
                
        return findPeak(nums, 0 ,len(nums)-1)