refer to: https://www.algoexpert.io/questions/Longest%20Peak

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Problem Statement

Sample

 

 

 Analysis

 

 Code

 1 def longestPeak(array):
 2     # Write your code here.
 3     longestPeakLength = 0
 4     i = 1 # the first one(index 0) can not be the peak
 5     while i < len(array) - 1: #check peak element
 6         isPeak = array[i-1] < array[i] and array[i] > array[i+1]
 7         if not isPeak:
 8             i += 1
 9             continue
10         leftIdx = i - 2 # expand the left side around peak
11         while leftIdx >=0 and array[leftIdx] < array[leftIdx + 1]:
12             leftIdx -= 1
13         rightIdx = i + 2# expand the right side around peak
14         while rightIdx < len(array) and array[rightIdx] < array[rightIdx - 1]:
15             rightIdx += 1
16         
17         currentPeakLength = rightIdx - leftIdx - 1 # calculate the length of current peak
18         longestPeakLength = max(longestPeakLength, currentPeakLength) # update the longest length of peak
19         i = rightIdx # update i, inside the rightIdx will be the part of calculated peak, we don't need to recalculate
20     return longestPeakLength
21             

Time and Space complexity

Time: O(N)-> outer loop. iterate the array once, inner loop, every element will be checked at most two or three times.(2N + 3N) -> O(N)

Space: O(1)