A peak element is an element that is greater than its neighbors. Given an input array where num[i] ≠ num[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 num[-1] = num[n] = -∞. For example, in array [1, 2, 3, 1], 3 is a peak e…

findpeak.py

class Solution(object):
    def findPeakElement(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        return self.findPeakRecur(nums, 0, len(nums)-1)
    
    def findPeakRecur(self, nums, lo, hi):
        mid = (lo + hi) // 2
        
        if (mid == 0 or nums[mid-1] < nums[mid]) and (mid == len(nums)-1 or nums[mid] > nums[mid+1]):
            return mid
        elif mid > 0 and nums[mid-1] > nums[mid]:
            return self.findPeakRecur(nums, lo, mid-1)
        elif mid < len(nums)-1 and nums[mid] < nums[mid+1]:
            return self.findPeakRecur(nums, mid+1, hi)
        
    def findPeakElementLinear(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        for i in range(len(nums)):
            if (i == 0 or nums[i-1] < nums[i]) and (i == len(nums)-1 or nums[i] > nums[i+1]):
                return i